diff --git a/src/libdredd/include_private/include/libdredd/mutate_visitor.h b/src/libdredd/include_private/include/libdredd/mutate_visitor.h
index 716e1135..d4313d5c 100644
--- a/src/libdredd/include_private/include/libdredd/mutate_visitor.h
+++ b/src/libdredd/include_private/include/libdredd/mutate_visitor.h
@@ -33,6 +33,7 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Frontend/CompilerInstance.h"
+#include "libdredd/mutation.h"
 #include "libdredd/mutation_tree_node.h"
 
 namespace dredd {
@@ -108,6 +109,11 @@ class MutateVisitor : public clang::RecursiveASTVisitor<MutateVisitor> {
     return constant_sized_arrays_to_rewrite_;
   }
 
+  [[nodiscard]] clang::SourceLocation
+  GetStartLocationOfFirstFunctionInSourceFile() const {
+    return start_location_of_first_function_in_source_file_;
+  }
+
  private:
   // Helper class that uses the RAII pattern to support pushing a new mutation
   // tree node on to the stack of mutation tree nodes used during visitation,
@@ -174,9 +180,21 @@ class MutateVisitor : public clang::RecursiveASTVisitor<MutateVisitor> {
   // this special case, so that it can be ignored.
   bool IsConversionOfEnumToConstructor(const clang::Expr& expr) const;
 
+  // It is safe to put Dredd's prelude before the first function we encounter in
+  // a file as Dredd only makes source code modifications inside functions.
+  void UpdateStartLocationOfFirstFunctionInSourceFile();
+
+  // Adds details of a mutation that can be applied, and performs associated
+  // bookkeeping.
+  void AddMutation(std::unique_ptr<Mutation> mutation);
+
   const clang::CompilerInstance* compiler_instance_;
   bool optimise_mutations_;
 
+  // Records the start location of the very first function definition in the
+  // source file, before which Dredd's prelude can be placed.
+  clang::SourceLocation start_location_of_first_function_in_source_file_;
+
   // Tracks the nest of declarations currently being traversed. Any new Dredd
   // functions will be put before the start of the current nest, which avoids
   // e.g. putting a Dredd function inside a class or function.
diff --git a/src/libdredd/src/mutate_ast_consumer.cc b/src/libdredd/src/mutate_ast_consumer.cc
index 4d237e50..3b3a9a08 100644
--- a/src/libdredd/src/mutate_ast_consumer.cc
+++ b/src/libdredd/src/mutate_ast_consumer.cc
@@ -137,12 +137,11 @@ void MutateAstConsumer::HandleTranslationUnit(clang::ASTContext& ast_context) {
 
   *mutation_info_->add_info_for_files() = mutation_info_for_file;
 
-  auto& source_manager = ast_context.getSourceManager();
-  const clang::SourceLocation start_of_source_file =
-      source_manager.translateLineCol(source_manager.getMainFileID(), 1, 1);
-  assert(start_of_source_file.isValid() &&
-         "There is at least one mutation, therefore the file must have some "
-         "content.");
+  const clang::SourceLocation start_location_of_first_function_in_source_file =
+      visitor_->GetStartLocationOfFirstFunctionInSourceFile();
+  assert(start_location_of_first_function_in_source_file.isValid() &&
+         "There is at least one mutation, therefore there must be at least one "
+         "function.");
 
   // Convert the unordered set Dredd declarations into an ordered set and add
   // them to the source file before the first declaration.
@@ -150,8 +149,8 @@ void MutateAstConsumer::HandleTranslationUnit(clang::ASTContext& ast_context) {
   sorted_dredd_declarations.insert(dredd_declarations.begin(),
                                    dredd_declarations.end());
   for (const auto& decl : sorted_dredd_declarations) {
-    const bool rewriter_result =
-        rewriter_.InsertTextBefore(start_of_source_file, decl);
+    const bool rewriter_result = rewriter_.InsertTextBefore(
+        start_location_of_first_function_in_source_file, decl);
     (void)rewriter_result;  // Keep release-mode compilers happy.
     assert(!rewriter_result && "Rewrite failed.\n");
   }
@@ -161,8 +160,8 @@ void MutateAstConsumer::HandleTranslationUnit(clang::ASTContext& ast_context) {
           ? GetDreddPreludeCpp(initial_mutation_id)
           : GetDreddPreludeC(initial_mutation_id);
 
-  bool rewriter_result =
-      rewriter_.InsertTextBefore(start_of_source_file, dredd_prelude);
+  bool rewriter_result = rewriter_.InsertTextBefore(
+      start_location_of_first_function_in_source_file, dredd_prelude);
   (void)rewriter_result;  // Keep release-mode compilers happy.
   assert(!rewriter_result && "Rewrite failed.\n");
 
diff --git a/src/libdredd/src/mutate_visitor.cc b/src/libdredd/src/mutate_visitor.cc
index c172fdfb..c1155f49 100644
--- a/src/libdredd/src/mutate_visitor.cc
+++ b/src/libdredd/src/mutate_visitor.cc
@@ -34,6 +34,7 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TypeTraits.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "libdredd/mutation.h"
@@ -63,6 +64,21 @@ bool MutateVisitor::IsTypeSupported(const clang::QualType qual_type) {
          (builtin_type->isInteger() || builtin_type->isFloatingPoint());
 }
 
+void MutateVisitor::UpdateStartLocationOfFirstFunctionInSourceFile() {
+  if (IsInFunction()) {
+    const clang::BeforeThanCompare<clang::SourceLocation> comparator(
+        compiler_instance_->getSourceManager());
+    auto source_range_in_main_file = GetSourceRangeInMainFile(
+        compiler_instance_->getPreprocessor(), *enclosing_decls_[0]);
+    if (start_location_of_first_function_in_source_file_.isInvalid() ||
+        comparator(source_range_in_main_file.getBegin(),
+                   start_location_of_first_function_in_source_file_)) {
+      start_location_of_first_function_in_source_file_ =
+          source_range_in_main_file.getBegin();
+    }
+  }
+}
+
 bool MutateVisitor::IsInFunction() {
   // Walk up the next of enclosing declarations
   for (int index = static_cast<int>(enclosing_decls_.size()) - 1; index >= 0;
@@ -352,10 +368,9 @@ void MutateVisitor::HandleUnaryOperator(clang::UnaryOperator* unary_operator) {
     }
   }
 
-  mutation_tree_path_.back()->AddMutation(
-      std::make_unique<MutationReplaceUnaryOperator>(
-          *unary_operator, compiler_instance_->getPreprocessor(),
-          compiler_instance_->getASTContext()));
+  AddMutation(std::make_unique<MutationReplaceUnaryOperator>(
+      *unary_operator, compiler_instance_->getPreprocessor(),
+      compiler_instance_->getASTContext()));
 }
 
 void MutateVisitor::HandleBinaryOperator(
@@ -415,10 +430,9 @@ void MutateVisitor::HandleBinaryOperator(
     return;
   }
 
-  mutation_tree_path_.back()->AddMutation(
-      std::make_unique<MutationReplaceBinaryOperator>(
-          *binary_operator, compiler_instance_->getPreprocessor(),
-          compiler_instance_->getASTContext()));
+  AddMutation(std::make_unique<MutationReplaceBinaryOperator>(
+      *binary_operator, compiler_instance_->getPreprocessor(),
+      compiler_instance_->getASTContext()));
 }
 
 void MutateVisitor::HandleExpr(clang::Expr* expr) {
@@ -508,7 +522,7 @@ void MutateVisitor::HandleExpr(clang::Expr* expr) {
     }
   }
 
-  mutation_tree_path_.back()->AddMutation(std::make_unique<MutationReplaceExpr>(
+  AddMutation(std::make_unique<MutationReplaceExpr>(
       *expr, compiler_instance_->getPreprocessor(),
       compiler_instance_->getASTContext()));
 }
@@ -555,6 +569,7 @@ bool MutateVisitor::VisitExpr(clang::Expr* expr) {
     return true;
   }
 
+  UpdateStartLocationOfFirstFunctionInSourceFile();
   if (auto* unary_operator = llvm::dyn_cast<clang::UnaryOperator>(expr)) {
     HandleUnaryOperator(unary_operator);
   }
@@ -621,14 +636,18 @@ bool MutateVisitor::TraverseCompoundStmt(clang::CompoundStmt* compound_stmt) {
     assert(!enclosing_decls_.empty() &&
            "Statements can only be removed if they are nested in some "
            "declaration.");
-    mutation_tree_path_.back()->AddMutation(
-        std::make_unique<MutationRemoveStmt>(
-            *target_stmt, compiler_instance_->getPreprocessor(),
-            compiler_instance_->getASTContext()));
+    AddMutation(std::make_unique<MutationRemoveStmt>(
+        *target_stmt, compiler_instance_->getPreprocessor(),
+        compiler_instance_->getASTContext()));
   }
   return true;
 }
 
+void MutateVisitor::AddMutation(std::unique_ptr<Mutation> mutation) {
+  UpdateStartLocationOfFirstFunctionInSourceFile();
+  mutation_tree_path_.back()->AddMutation(std::move(mutation));
+}
+
 bool MutateVisitor::VisitVarDecl(clang::VarDecl* var_decl) {
   var_decl_source_locations_.insert(var_decl->getLocation());
   return true;
diff --git a/test/single_file/add_type_aliases.c.noopt.expected b/test/single_file/add_type_aliases.c.noopt.expected
index 3faf287f..8638812e 100644
--- a/test/single_file/add_type_aliases.c.noopt.expected
+++ b/test/single_file/add_type_aliases.c.noopt.expected
@@ -1,3 +1,6 @@
+#include <inttypes.h>
+#include <stddef.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -152,9 +155,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int(int arg1, int a
   return arg1 + arg2;
 }
 
-#include <inttypes.h>
-#include <stddef.h>
-
 int main() {
   unsigned a;
   uint32_t b;
diff --git a/test/single_file/add_type_aliases.cc.noopt.expected b/test/single_file/add_type_aliases.cc.noopt.expected
index b227f0b0..4c54400b 100644
--- a/test/single_file/add_type_aliases.cc.noopt.expected
+++ b/test/single_file/add_type_aliases.cc.noopt.expected
@@ -1,3 +1,6 @@
+#include <cinttypes>
+#include <cstddef>
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -154,9 +157,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int(int arg1, int a
   return arg1 + arg2;
 }
 
-#include <cinttypes>
-#include <cstddef>
-
 int main() {
   unsigned a;
   uint32_t b;
diff --git a/test/single_file/bitfield.c.expected b/test/single_file/bitfield.c.expected
index 91dd511e..5626020c 100644
--- a/test/single_file/bitfield.c.expected
+++ b/test/single_file/bitfield.c.expected
@@ -1,3 +1,8 @@
+struct S {
+  int a : 3;
+  int b : 3;
+};
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -58,11 +63,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-struct S {
-  int a : 3;
-  int b : 3;
-};
-
 void foo() {
   struct S myS;
   if (!__dredd_enabled_mutation(6)) { myS.a = __dredd_replace_expr_int(myS.b, 0); }
diff --git a/test/single_file/bitfield.c.noopt.expected b/test/single_file/bitfield.c.noopt.expected
index 16bb947f..fe020fde 100644
--- a/test/single_file/bitfield.c.noopt.expected
+++ b/test/single_file/bitfield.c.noopt.expected
@@ -1,3 +1,8 @@
+struct S {
+  int a : 3;
+  int b : 3;
+};
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -59,11 +64,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-struct S {
-  int a : 3;
-  int b : 3;
-};
-
 void foo() {
   struct S myS;
   if (!__dredd_enabled_mutation(12)) { __dredd_replace_expr_int(myS.a = __dredd_replace_expr_int(myS.b, 0), 6); }
diff --git a/test/single_file/bitfield.cc.expected b/test/single_file/bitfield.cc.expected
index 93026006..b289631f 100644
--- a/test/single_file/bitfield.cc.expected
+++ b/test/single_file/bitfield.cc.expected
@@ -1,3 +1,8 @@
+struct S {
+  int a : 3;
+  int b : 3;
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -60,11 +65,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-struct S {
-  int a : 3;
-  int b : 3;
-};
-
 void foo() {
   S myS;
   if (!__dredd_enabled_mutation(6)) { myS.a = __dredd_replace_expr_int(myS.b, 0); }
diff --git a/test/single_file/bitfield.cc.noopt.expected b/test/single_file/bitfield.cc.noopt.expected
index 027e52cc..307a28e6 100644
--- a/test/single_file/bitfield.cc.noopt.expected
+++ b/test/single_file/bitfield.cc.noopt.expected
@@ -1,3 +1,8 @@
+struct S {
+  int a : 3;
+  int b : 3;
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -72,11 +77,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-struct S {
-  int a : 3;
-  int b : 3;
-};
-
 void foo() {
   S myS;
   if (!__dredd_enabled_mutation(6)) { myS.a = __dredd_replace_expr_int(myS.b, 0); }
diff --git a/test/single_file/bitfield_reference_passing.cc.expected b/test/single_file/bitfield_reference_passing.cc.expected
index ada685ae..c74bfb9d 100644
--- a/test/single_file/bitfield_reference_passing.cc.expected
+++ b/test/single_file/bitfield_reference_passing.cc.expected
@@ -1,3 +1,9 @@
+template<typename T> void bloop(T& x) { }
+
+struct foo {
+  int b : 2;
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -42,12 +48,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
 }
 
-template<typename T> void bloop(T& x) { }
-
-struct foo {
-  int b : 2;
-};
-
 int main() {
   const foo d = foo();
   if (!__dredd_enabled_mutation(0)) { bloop(d.b); }
diff --git a/test/single_file/bitfield_reference_passing.cc.noopt.expected b/test/single_file/bitfield_reference_passing.cc.noopt.expected
index ada685ae..c74bfb9d 100644
--- a/test/single_file/bitfield_reference_passing.cc.noopt.expected
+++ b/test/single_file/bitfield_reference_passing.cc.noopt.expected
@@ -1,3 +1,9 @@
+template<typename T> void bloop(T& x) { }
+
+struct foo {
+  int b : 2;
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -42,12 +48,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
 }
 
-template<typename T> void bloop(T& x) { }
-
-struct foo {
-  int b : 2;
-};
-
 int main() {
   const foo d = foo();
   if (!__dredd_enabled_mutation(0)) { bloop(d.b); }
diff --git a/test/single_file/boolean_not_insertion_optimisation.c.expected b/test/single_file/boolean_not_insertion_optimisation.c.expected
index 57097292..7d24d8a9 100644
--- a/test/single_file/boolean_not_insertion_optimisation.c.expected
+++ b/test/single_file/boolean_not_insertion_optimisation.c.expected
@@ -1,3 +1,5 @@
+#include <stdbool.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -71,8 +73,6 @@ static int __dredd_replace_binary_operator_LAnd_arg1_int_arg2_int_rhs_zero_lhs_o
   if (__dredd_enabled_mutation(local_mutation_id + 2)) return 1;
   return arg;
 }
-#include <stdbool.h>
-
 int main() {
   int x = __dredd_replace_expr_int_zero(__dredd_replace_binary_operator_LAnd_arg1_int_arg2_int_rhs_zero_lhs_one_outer(__dredd_replace_binary_operator_LAnd_arg1_int_arg2_int_rhs_zero_lhs_one_lhs(__dredd_replace_expr_int_one(1, 0), 5) && __dredd_replace_binary_operator_LAnd_arg1_int_arg2_int_rhs_zero_lhs_one_rhs(__dredd_replace_expr_int_zero(0, 3), 5), 5), 8);
 }
diff --git a/test/single_file/boolean_not_insertion_optimisation.c.noopt.expected b/test/single_file/boolean_not_insertion_optimisation.c.noopt.expected
index ead86198..9e643830 100644
--- a/test/single_file/boolean_not_insertion_optimisation.c.noopt.expected
+++ b/test/single_file/boolean_not_insertion_optimisation.c.noopt.expected
@@ -1,3 +1,5 @@
+#include <stdbool.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -67,8 +69,6 @@ static int __dredd_replace_binary_operator_LAnd_arg1_int_arg2_int_lhs(int arg, i
   if (__dredd_enabled_mutation(local_mutation_id + 2)) return 1;
   return arg;
 }
-#include <stdbool.h>
-
 int main() {
   int x = __dredd_replace_expr_int(__dredd_replace_binary_operator_LAnd_arg1_int_arg2_int_outer(__dredd_replace_binary_operator_LAnd_arg1_int_arg2_int_lhs(__dredd_replace_expr_int(1, 0), 12) && __dredd_replace_binary_operator_LAnd_arg1_int_arg2_int_rhs(__dredd_replace_expr_int(0, 6), 12), 12), 15);
 }
diff --git a/test/single_file/comment.cc.expected b/test/single_file/comment.cc.expected
index a73eb888..19a9681b 100644
--- a/test/single_file/comment.cc.expected
+++ b/test/single_file/comment.cc.expected
@@ -1,3 +1,5 @@
+void g();
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -48,8 +50,6 @@ static bool __dredd_replace_expr_bool_true(bool arg, int local_mutation_id) {
   return arg;
 }
 
-void g();
-
 void f()
 {
   if (!__dredd_enabled_mutation(0)) { g() /* something */ ; }
diff --git a/test/single_file/comment.cc.noopt.expected b/test/single_file/comment.cc.noopt.expected
index ce5e7b68..6e5d6935 100644
--- a/test/single_file/comment.cc.noopt.expected
+++ b/test/single_file/comment.cc.noopt.expected
@@ -1,3 +1,5 @@
+void g();
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -50,8 +52,6 @@ static bool __dredd_replace_expr_bool(bool arg, int local_mutation_id) {
   return arg;
 }
 
-void g();
-
 void f()
 {
   if (!__dredd_enabled_mutation(0)) { g() /* something */ ; }
diff --git a/test/single_file/comment_at_start_of_file.cc.expected b/test/single_file/comment_at_start_of_file.cc.expected
index 903c91ac..550e08bd 100644
--- a/test/single_file/comment_at_start_of_file.cc.expected
+++ b/test/single_file/comment_at_start_of_file.cc.expected
@@ -1,3 +1,5 @@
+// Hello
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -52,8 +54,6 @@ static int __dredd_replace_expr_int_constant(int arg, int local_mutation_id) {
   return arg;
 }
 
-// Hello
-
 int main() {
   if (!__dredd_enabled_mutation(5)) { return __dredd_replace_expr_int_constant(42, 0); }
 }
diff --git a/test/single_file/comment_at_start_of_file.cc.noopt.expected b/test/single_file/comment_at_start_of_file.cc.noopt.expected
index 1c530885..68d9502e 100644
--- a/test/single_file/comment_at_start_of_file.cc.noopt.expected
+++ b/test/single_file/comment_at_start_of_file.cc.noopt.expected
@@ -1,3 +1,5 @@
+// Hello
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -53,8 +55,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-// Hello
-
 int main() {
   if (!__dredd_enabled_mutation(6)) { return __dredd_replace_expr_int(42, 0); }
 }
diff --git a/test/single_file/const_expr_function.cc.expected b/test/single_file/const_expr_function.cc.expected
index 9c2e5174..9b424ea0 100644
--- a/test/single_file/const_expr_function.cc.expected
+++ b/test/single_file/const_expr_function.cc.expected
@@ -1,3 +1,5 @@
+constexpr int Max(int a, int b) { return a > b ? a : b; }
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -52,8 +54,6 @@ static int __dredd_replace_expr_int_constant(int arg, int local_mutation_id) {
   return arg;
 }
 
-constexpr int Max(int a, int b) { return a > b ? a : b; }
-
 int main() {
   if (!__dredd_enabled_mutation(10)) { Max(__dredd_replace_expr_int_constant(5, 0),__dredd_replace_expr_int_constant(4, 5)); }
 }
diff --git a/test/single_file/const_expr_function.cc.noopt.expected b/test/single_file/const_expr_function.cc.noopt.expected
index 2b4e1832..80c68a83 100644
--- a/test/single_file/const_expr_function.cc.noopt.expected
+++ b/test/single_file/const_expr_function.cc.noopt.expected
@@ -1,3 +1,5 @@
+constexpr int Max(int a, int b) { return a > b ? a : b; }
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -64,8 +66,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-constexpr int Max(int a, int b) { return a > b ? a : b; }
-
 int main() {
   if (!__dredd_enabled_mutation(18)) { __dredd_replace_expr_int([&]() -> int { return Max(__dredd_replace_expr_int(5, 0),__dredd_replace_expr_int(4, 6)); }, 12); }
 }
diff --git a/test/single_file/const_expr_function_call.cc.expected b/test/single_file/const_expr_function_call.cc.expected
index 84deb5c0..cf11e652 100644
--- a/test/single_file/const_expr_function_call.cc.expected
+++ b/test/single_file/const_expr_function_call.cc.expected
@@ -1,3 +1,5 @@
+constexpr int Max(int a, int b) { return a > b ? a : b; }
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -62,8 +64,6 @@ static int __dredd_replace_expr_int_constant(int arg, int local_mutation_id) {
   return arg;
 }
 
-constexpr int Max(int a, int b) { return a > b ? a : b; }
-
 int foo() {
   if (!__dredd_enabled_mutation(15)) { return __dredd_replace_expr_int_constant([&]() -> int { return Max(__dredd_replace_expr_int_constant(5, 0),__dredd_replace_expr_int_constant(4, 5)); }, 10); }
 }
diff --git a/test/single_file/const_expr_function_call.cc.noopt.expected b/test/single_file/const_expr_function_call.cc.noopt.expected
index 078ac89a..34a2606c 100644
--- a/test/single_file/const_expr_function_call.cc.noopt.expected
+++ b/test/single_file/const_expr_function_call.cc.noopt.expected
@@ -1,3 +1,5 @@
+constexpr int Max(int a, int b) { return a > b ? a : b; }
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -64,8 +66,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-constexpr int Max(int a, int b) { return a > b ? a : b; }
-
 int foo() {
   if (!__dredd_enabled_mutation(18)) { return __dredd_replace_expr_int([&]() -> int { return Max(__dredd_replace_expr_int(5, 0),__dredd_replace_expr_int(4, 6)); }, 12); }
 }
diff --git a/test/single_file/constexpr_if1.cc.expected b/test/single_file/constexpr_if1.cc.expected
index 0116a359..0c1d025a 100644
--- a/test/single_file/constexpr_if1.cc.expected
+++ b/test/single_file/constexpr_if1.cc.expected
@@ -1,3 +1,5 @@
+#include <iostream>
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -42,8 +44,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
 }
 
-#include <iostream>
-
 template <int a> void foo() {
   if (!__dredd_enabled_mutation(1)) { if constexpr (a) {
     if (!__dredd_enabled_mutation(0)) { std::cout << "Hi"; }
diff --git a/test/single_file/constexpr_if1.cc.noopt.expected b/test/single_file/constexpr_if1.cc.noopt.expected
index 2e7bbb30..4e0e6867 100644
--- a/test/single_file/constexpr_if1.cc.noopt.expected
+++ b/test/single_file/constexpr_if1.cc.noopt.expected
@@ -1,3 +1,5 @@
+#include <iostream>
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -42,8 +44,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
 }
 
-#include <iostream>
-
 template <int a> void foo() {
   if (!__dredd_enabled_mutation(1)) { if constexpr (a) {
     if (!__dredd_enabled_mutation(0)) { std::cout << "Hi"; }
diff --git a/test/single_file/construct_struct_from_enum_constant.cc.expected b/test/single_file/construct_struct_from_enum_constant.cc.expected
index ebddef71..45d3b6b7 100644
--- a/test/single_file/construct_struct_from_enum_constant.cc.expected
+++ b/test/single_file/construct_struct_from_enum_constant.cc.expected
@@ -1,3 +1,10 @@
+struct foo {
+  foo(int) {};
+  operator int();
+};
+
+enum baz { bar };
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -55,13 +62,6 @@ static bool __dredd_replace_expr_bool_false(bool arg, int local_mutation_id) {
   return arg;
 }
 
-struct foo {
-  foo(int) {};
-  operator int();
-};
-
-enum baz { bar };
-
 int main() { 
   if (!__dredd_enabled_mutation(3)) { __dredd_replace_expr_bool_false(0, 0) ? foo(__dredd_replace_expr_int_zero(0, 1)) : baz::bar; }
 }
diff --git a/test/single_file/construct_struct_from_enum_constant.cc.noopt.expected b/test/single_file/construct_struct_from_enum_constant.cc.noopt.expected
index f8834fd4..b390bea8 100644
--- a/test/single_file/construct_struct_from_enum_constant.cc.noopt.expected
+++ b/test/single_file/construct_struct_from_enum_constant.cc.noopt.expected
@@ -1,3 +1,10 @@
+struct foo {
+  foo(int) {};
+  operator int();
+};
+
+enum baz { bar };
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -61,13 +68,6 @@ static bool __dredd_replace_expr_bool(bool arg, int local_mutation_id) {
   return arg;
 }
 
-struct foo {
-  foo(int) {};
-  operator int();
-};
-
-enum baz { bar };
-
 int main() { 
   if (!__dredd_enabled_mutation(15)) { __dredd_replace_expr_bool(__dredd_replace_expr_int(0, 0), 6) ? foo(__dredd_replace_expr_int(0, 9)) : baz::bar; }
 }
diff --git a/test/single_file/define_at_start_of_file.c.expected b/test/single_file/define_at_start_of_file.c.expected
index aa415de3..6ca5c388 100644
--- a/test/single_file/define_at_start_of_file.c.expected
+++ b/test/single_file/define_at_start_of_file.c.expected
@@ -1,3 +1,6 @@
+#define API
+API int func1();
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -48,7 +51,4 @@ static int __dredd_replace_expr_int_one(int arg, int local_mutation_id) {
   return arg;
 }
 
-#define API
-API int func1();
-
 int main() { int a = __dredd_replace_expr_int_one(1, 0); }
diff --git a/test/single_file/define_at_start_of_file.c.noopt.expected b/test/single_file/define_at_start_of_file.c.noopt.expected
index b47b64b8..69e3d2cd 100644
--- a/test/single_file/define_at_start_of_file.c.noopt.expected
+++ b/test/single_file/define_at_start_of_file.c.noopt.expected
@@ -1,3 +1,6 @@
+#define API
+API int func1();
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -51,7 +54,4 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#define API
-API int func1();
-
 int main() { int a = __dredd_replace_expr_int(1, 0); }
diff --git a/test/single_file/define_in_first_decl.c.expected b/test/single_file/define_in_first_decl.c.expected
index 62165a5f..0f3b6528 100644
--- a/test/single_file/define_in_first_decl.c.expected
+++ b/test/single_file/define_in_first_decl.c.expected
@@ -1,3 +1,5 @@
+#define TYPE int
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -67,8 +69,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int_lhs_one(int arg
   return arg1 + arg2;
 }
 
-#define TYPE int
-
 TYPE foo() {
   if (!__dredd_enabled_mutation(17)) { return __dredd_replace_expr_int_constant(__dredd_replace_binary_operator_Add_arg1_int_arg2_int_lhs_one(__dredd_replace_expr_int_one(1, 0) , __dredd_replace_expr_int_constant(2, 3), 8), 12); }
 }
diff --git a/test/single_file/define_in_first_decl.c.noopt.expected b/test/single_file/define_in_first_decl.c.noopt.expected
index e87b6686..06d07f52 100644
--- a/test/single_file/define_in_first_decl.c.noopt.expected
+++ b/test/single_file/define_in_first_decl.c.noopt.expected
@@ -1,3 +1,5 @@
+#define TYPE int
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -62,8 +64,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int(int arg1, int a
   return arg1 + arg2;
 }
 
-#define TYPE int
-
 TYPE foo() {
   if (!__dredd_enabled_mutation(24)) { return __dredd_replace_expr_int(__dredd_replace_binary_operator_Add_arg1_int_arg2_int(__dredd_replace_expr_int(1, 0) , __dredd_replace_expr_int(2, 6), 12), 18); }
 }
diff --git a/test/single_file/define_in_first_decl.cc.expected b/test/single_file/define_in_first_decl.cc.expected
index ae5e1fba..fc982b8d 100644
--- a/test/single_file/define_in_first_decl.cc.expected
+++ b/test/single_file/define_in_first_decl.cc.expected
@@ -1,3 +1,5 @@
+#define TYPE int
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -69,8 +71,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int_lhs_one(int arg
   return arg1 + arg2;
 }
 
-#define TYPE int
-
 TYPE foo() {
   if (!__dredd_enabled_mutation(17)) { return __dredd_replace_expr_int_constant(__dredd_replace_binary_operator_Add_arg1_int_arg2_int_lhs_one(__dredd_replace_expr_int_one(1, 0) , __dredd_replace_expr_int_constant(2, 3), 8), 12); }
 }
diff --git a/test/single_file/define_in_first_decl.cc.noopt.expected b/test/single_file/define_in_first_decl.cc.noopt.expected
index 13600fc3..3122053e 100644
--- a/test/single_file/define_in_first_decl.cc.noopt.expected
+++ b/test/single_file/define_in_first_decl.cc.noopt.expected
@@ -1,3 +1,5 @@
+#define TYPE int
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -64,8 +66,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int(int arg1, int a
   return arg1 + arg2;
 }
 
-#define TYPE int
-
 TYPE foo() {
   if (!__dredd_enabled_mutation(24)) { return __dredd_replace_expr_int(__dredd_replace_binary_operator_Add_arg1_int_arg2_int(__dredd_replace_expr_int(1, 0) , __dredd_replace_expr_int(2, 6), 12), 18); }
 }
diff --git a/test/single_file/enum.c.noopt.expected b/test/single_file/enum.c.noopt.expected
index 1a0d6983..224d9cf2 100644
--- a/test/single_file/enum.c.noopt.expected
+++ b/test/single_file/enum.c.noopt.expected
@@ -1,3 +1,8 @@
+enum A {
+  X,
+  Y
+};
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -51,11 +56,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-enum A {
-  X,
-  Y
-};
-
 void foo() {
   enum A myA = __dredd_replace_expr_int(X, 0);
 }
diff --git a/test/single_file/expr_macro.c.expected b/test/single_file/expr_macro.c.expected
index 5b9f9615..d9356d05 100644
--- a/test/single_file/expr_macro.c.expected
+++ b/test/single_file/expr_macro.c.expected
@@ -1,3 +1,7 @@
+#define E (1, 2, 3)
+
+void foo(int, int, int);
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -40,10 +44,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return enabled_bitset[local_mutation_id / 64] & ((uint64_t) 1 << (local_mutation_id % 64));
 }
 
-#define E (1, 2, 3)
-
-void foo(int, int, int);
-
 int main() {
   if (!__dredd_enabled_mutation(0)) { foo E; }
 }
diff --git a/test/single_file/expr_macro.c.noopt.expected b/test/single_file/expr_macro.c.noopt.expected
index 5b9f9615..d9356d05 100644
--- a/test/single_file/expr_macro.c.noopt.expected
+++ b/test/single_file/expr_macro.c.noopt.expected
@@ -1,3 +1,7 @@
+#define E (1, 2, 3)
+
+void foo(int, int, int);
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -40,10 +44,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return enabled_bitset[local_mutation_id / 64] & ((uint64_t) 1 << (local_mutation_id % 64));
 }
 
-#define E (1, 2, 3)
-
-void foo(int, int, int);
-
 int main() {
   if (!__dredd_enabled_mutation(0)) { foo E; }
 }
diff --git a/test/single_file/expr_macro.cc.expected b/test/single_file/expr_macro.cc.expected
index e7e0605e..4a8cd46f 100644
--- a/test/single_file/expr_macro.cc.expected
+++ b/test/single_file/expr_macro.cc.expected
@@ -1,3 +1,7 @@
+#define E (1, 2, 3)
+
+void foo(int, int, int);
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -42,10 +46,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
 }
 
-#define E (1, 2, 3)
-
-void foo(int, int, int);
-
 int main() {
   if (!__dredd_enabled_mutation(0)) { foo E; }
 }
diff --git a/test/single_file/expr_macro.cc.noopt.expected b/test/single_file/expr_macro.cc.noopt.expected
index e7e0605e..4a8cd46f 100644
--- a/test/single_file/expr_macro.cc.noopt.expected
+++ b/test/single_file/expr_macro.cc.noopt.expected
@@ -1,3 +1,7 @@
+#define E (1, 2, 3)
+
+void foo(int, int, int);
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -42,10 +46,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
 }
 
-#define E (1, 2, 3)
-
-void foo(int, int, int);
-
 int main() {
   if (!__dredd_enabled_mutation(0)) { foo E; }
 }
diff --git a/test/single_file/initializer_list.cc.expected b/test/single_file/initializer_list.cc.expected
index 4ac38bf1..7ac404e4 100644
--- a/test/single_file/initializer_list.cc.expected
+++ b/test/single_file/initializer_list.cc.expected
@@ -1,3 +1,12 @@
+#include <cstddef>
+
+struct A {
+  size_t x;
+  size_t y;
+};
+
+void foo(A arg);
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -49,15 +58,6 @@ static int __dredd_replace_expr_int_zero(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <cstddef>
-
-struct A {
-  size_t x;
-  size_t y;
-};
-
-void foo(A arg);
-
 void bar() {
   if (!__dredd_enabled_mutation(4)) { foo({static_cast<unsigned long>(__dredd_replace_expr_int_zero(0, 0)), static_cast<unsigned long>(__dredd_replace_expr_int_zero(0, 2))}); }
 }
diff --git a/test/single_file/initializer_list.cc.noopt.expected b/test/single_file/initializer_list.cc.noopt.expected
index 9879e886..7227c4c1 100644
--- a/test/single_file/initializer_list.cc.noopt.expected
+++ b/test/single_file/initializer_list.cc.noopt.expected
@@ -1,3 +1,12 @@
+#include <cstddef>
+
+struct A {
+  size_t x;
+  size_t y;
+};
+
+void foo(A arg);
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -53,15 +62,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <cstddef>
-
-struct A {
-  size_t x;
-  size_t y;
-};
-
-void foo(A arg);
-
 void bar() {
   if (!__dredd_enabled_mutation(12)) { foo({static_cast<unsigned long>(__dredd_replace_expr_int(0, 0)), static_cast<unsigned long>(__dredd_replace_expr_int(0, 6))}); }
 }
diff --git a/test/single_file/initializer_list_long_to_short.cc.expected b/test/single_file/initializer_list_long_to_short.cc.expected
index 6d947cb9..885e495f 100644
--- a/test/single_file/initializer_list_long_to_short.cc.expected
+++ b/test/single_file/initializer_list_long_to_short.cc.expected
@@ -1,3 +1,10 @@
+#include <initializer_list>
+
+class foo {
+public:
+  foo(std::initializer_list<short>) {}
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -52,13 +59,6 @@ static long __dredd_replace_expr_long_constant(long arg, int local_mutation_id)
   return arg;
 }
 
-#include <initializer_list>
-
-class foo {
-public:
-  foo(std::initializer_list<short>) {}
-};
-
 int main() { 
     if (!__dredd_enabled_mutation(5)) { foo{static_cast<short>(__dredd_replace_expr_long_constant((long) 2, 0))}; } 
 }
diff --git a/test/single_file/initializer_list_long_to_short.cc.noopt.expected b/test/single_file/initializer_list_long_to_short.cc.noopt.expected
index adad602d..98132b39 100644
--- a/test/single_file/initializer_list_long_to_short.cc.noopt.expected
+++ b/test/single_file/initializer_list_long_to_short.cc.noopt.expected
@@ -1,3 +1,10 @@
+#include <initializer_list>
+
+class foo {
+public:
+  foo(std::initializer_list<short>) {}
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -64,13 +71,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <initializer_list>
-
-class foo {
-public:
-  foo(std::initializer_list<short>) {}
-};
-
 int main() { 
     if (!__dredd_enabled_mutation(18)) { foo{static_cast<short>(__dredd_replace_expr_long((long) __dredd_replace_expr_long(__dredd_replace_expr_int(2, 0), 6), 12))}; } 
 }
diff --git a/test/single_file/initializer_list_narrower.cc.expected b/test/single_file/initializer_list_narrower.cc.expected
index b889f5f0..8a3fd4f7 100644
--- a/test/single_file/initializer_list_narrower.cc.expected
+++ b/test/single_file/initializer_list_narrower.cc.expected
@@ -1,3 +1,10 @@
+#include <initializer_list>
+
+class foo {
+public:
+  foo(std::initializer_list<unsigned int>) {}
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -52,13 +59,6 @@ static int __dredd_replace_expr_int_constant(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <initializer_list>
-
-class foo {
-public:
-  foo(std::initializer_list<unsigned int>) {}
-};
-
 int main() { 
     if (!__dredd_enabled_mutation(10)) { foo{static_cast<unsigned int>(__dredd_replace_expr_int_constant(+__dredd_replace_expr_int_constant(2, 0), 5))}; } 
 }
diff --git a/test/single_file/initializer_list_narrower.cc.noopt.expected b/test/single_file/initializer_list_narrower.cc.noopt.expected
index b6b41541..5287984a 100644
--- a/test/single_file/initializer_list_narrower.cc.noopt.expected
+++ b/test/single_file/initializer_list_narrower.cc.noopt.expected
@@ -1,3 +1,10 @@
+#include <initializer_list>
+
+class foo {
+public:
+  foo(std::initializer_list<unsigned int>) {}
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -53,13 +60,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <initializer_list>
-
-class foo {
-public:
-  foo(std::initializer_list<unsigned int>) {}
-};
-
 int main() { 
     if (!__dredd_enabled_mutation(12)) { foo{static_cast<unsigned int>(__dredd_replace_expr_int(+__dredd_replace_expr_int(2, 0), 6))}; } 
 }
diff --git a/test/single_file/misc004.cc b/test/single_file/misc004.cc
new file mode 100644
index 00000000..ee3ad5ac
--- /dev/null
+++ b/test/single_file/misc004.cc
@@ -0,0 +1,7 @@
+#if defined(__GLIBC__) && !defined(__FreeBSD_kernel__) &&  defined(__CONFIG_H__)
+#  error test.h must be #included before system headers
+#endif
+
+int main() {
+    int x = 1 + 2;
+}
diff --git a/test/single_file/misc004.cc.expected b/test/single_file/misc004.cc.expected
new file mode 100644
index 00000000..55c380bd
--- /dev/null
+++ b/test/single_file/misc004.cc.expected
@@ -0,0 +1,78 @@
+#if defined(__GLIBC__) && !defined(__FreeBSD_kernel__) &&  defined(__CONFIG_H__)
+#  error test.h must be #included before system headers
+#endif
+
+#include <cinttypes>
+#include <cstddef>
+#include <functional>
+#include <string>
+
+
+#ifdef _MSC_VER
+#define thread_local __declspec(thread)
+#elif __APPLE__
+#define thread_local __thread
+#endif
+
+static thread_local bool __dredd_some_mutation_enabled = true;
+static bool __dredd_enabled_mutation(int local_mutation_id) {
+  static thread_local bool initialized = false;
+  static thread_local uint64_t enabled_bitset[1];
+  if (!initialized) {
+    bool some_mutation_enabled = false;
+    const char* dredd_environment_variable = std::getenv("DREDD_ENABLED_MUTATION");
+    if (dredd_environment_variable != nullptr) {
+      std::string contents(dredd_environment_variable);
+      while (true) {
+        size_t pos = contents.find(",");
+        std::string token = (pos == std::string::npos ? contents : contents.substr(0, pos));
+        if (!token.empty()) {
+          int value = std::stoi(token);
+          int local_value = value - 0;
+          if (local_value >= 0 && local_value < 17) {
+            enabled_bitset[local_value / 64] |= (static_cast<uint64_t>(1) << (local_value % 64));
+            some_mutation_enabled = true;
+          }
+        }
+        if (pos == std::string::npos) {
+          break;
+        }
+        contents.erase(0, pos + 1);
+      }
+    }
+    initialized = true;
+    __dredd_some_mutation_enabled = some_mutation_enabled;
+  }
+  return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
+}
+
+static int __dredd_replace_expr_int_one(int arg, int local_mutation_id) {
+  if (!__dredd_some_mutation_enabled) return arg;
+  if (__dredd_enabled_mutation(local_mutation_id + 0)) return ~(arg);
+  if (__dredd_enabled_mutation(local_mutation_id + 1)) return 0;
+  if (__dredd_enabled_mutation(local_mutation_id + 2)) return -1;
+  return arg;
+}
+
+static int __dredd_replace_expr_int_constant(int arg, int local_mutation_id) {
+  if (!__dredd_some_mutation_enabled) return arg;
+  if (__dredd_enabled_mutation(local_mutation_id + 0)) return ~(arg);
+  if (__dredd_enabled_mutation(local_mutation_id + 1)) return -(arg);
+  if (__dredd_enabled_mutation(local_mutation_id + 2)) return 0;
+  if (__dredd_enabled_mutation(local_mutation_id + 3)) return 1;
+  if (__dredd_enabled_mutation(local_mutation_id + 4)) return -1;
+  return arg;
+}
+
+static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int_lhs_one(int arg1, int arg2, int local_mutation_id) {
+  if (!__dredd_some_mutation_enabled) return arg1 + arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 0)) return arg1 / arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 1)) return arg1 % arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 2)) return arg1 - arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 3)) return arg2;
+  return arg1 + arg2;
+}
+
+int main() {
+    int x = __dredd_replace_expr_int_constant(__dredd_replace_binary_operator_Add_arg1_int_arg2_int_lhs_one(__dredd_replace_expr_int_one(1, 0) , __dredd_replace_expr_int_constant(2, 3), 8), 12);
+}
diff --git a/test/single_file/misc004.cc.noopt.expected b/test/single_file/misc004.cc.noopt.expected
new file mode 100644
index 00000000..bc601fbd
--- /dev/null
+++ b/test/single_file/misc004.cc.noopt.expected
@@ -0,0 +1,73 @@
+#if defined(__GLIBC__) && !defined(__FreeBSD_kernel__) &&  defined(__CONFIG_H__)
+#  error test.h must be #included before system headers
+#endif
+
+#include <cinttypes>
+#include <cstddef>
+#include <functional>
+#include <string>
+
+
+#ifdef _MSC_VER
+#define thread_local __declspec(thread)
+#elif __APPLE__
+#define thread_local __thread
+#endif
+
+static thread_local bool __dredd_some_mutation_enabled = true;
+static bool __dredd_enabled_mutation(int local_mutation_id) {
+  static thread_local bool initialized = false;
+  static thread_local uint64_t enabled_bitset[1];
+  if (!initialized) {
+    bool some_mutation_enabled = false;
+    const char* dredd_environment_variable = std::getenv("DREDD_ENABLED_MUTATION");
+    if (dredd_environment_variable != nullptr) {
+      std::string contents(dredd_environment_variable);
+      while (true) {
+        size_t pos = contents.find(",");
+        std::string token = (pos == std::string::npos ? contents : contents.substr(0, pos));
+        if (!token.empty()) {
+          int value = std::stoi(token);
+          int local_value = value - 0;
+          if (local_value >= 0 && local_value < 24) {
+            enabled_bitset[local_value / 64] |= (static_cast<uint64_t>(1) << (local_value % 64));
+            some_mutation_enabled = true;
+          }
+        }
+        if (pos == std::string::npos) {
+          break;
+        }
+        contents.erase(0, pos + 1);
+      }
+    }
+    initialized = true;
+    __dredd_some_mutation_enabled = some_mutation_enabled;
+  }
+  return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
+}
+
+static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
+  if (!__dredd_some_mutation_enabled) return arg;
+  if (__dredd_enabled_mutation(local_mutation_id + 0)) return !(arg);
+  if (__dredd_enabled_mutation(local_mutation_id + 1)) return ~(arg);
+  if (__dredd_enabled_mutation(local_mutation_id + 2)) return -(arg);
+  if (__dredd_enabled_mutation(local_mutation_id + 3)) return 0;
+  if (__dredd_enabled_mutation(local_mutation_id + 4)) return 1;
+  if (__dredd_enabled_mutation(local_mutation_id + 5)) return -1;
+  return arg;
+}
+
+static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int(int arg1, int arg2, int local_mutation_id) {
+  if (!__dredd_some_mutation_enabled) return arg1 + arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 0)) return arg1 / arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 1)) return arg1 * arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 2)) return arg1 % arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 3)) return arg1 - arg2;
+  if (__dredd_enabled_mutation(local_mutation_id + 4)) return arg1;
+  if (__dredd_enabled_mutation(local_mutation_id + 5)) return arg2;
+  return arg1 + arg2;
+}
+
+int main() {
+    int x = __dredd_replace_expr_int(__dredd_replace_binary_operator_Add_arg1_int_arg2_int(__dredd_replace_expr_int(1, 0) , __dredd_replace_expr_int(2, 6), 12), 18);
+}
diff --git a/test/single_file/new_expr_array_size.cc.expected b/test/single_file/new_expr_array_size.cc.expected
index f3af4be2..cbd9e7af 100644
--- a/test/single_file/new_expr_array_size.cc.expected
+++ b/test/single_file/new_expr_array_size.cc.expected
@@ -1,3 +1,8 @@
+class foo {
+public:
+  foo(int x) {}
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -52,11 +57,6 @@ static int __dredd_replace_expr_int_constant(int arg, int local_mutation_id) {
   return arg;
 }
 
-class foo {
-public:
-  foo(int x) {}
-};
-
 int main() { 
   if (!__dredd_enabled_mutation(10)) { new foo[2]{__dredd_replace_expr_int_constant(4, 0), __dredd_replace_expr_int_constant(5, 5)}; } 
 }
diff --git a/test/single_file/new_expr_array_size.cc.noopt.expected b/test/single_file/new_expr_array_size.cc.noopt.expected
index dbb038b1..f4ecebae 100644
--- a/test/single_file/new_expr_array_size.cc.noopt.expected
+++ b/test/single_file/new_expr_array_size.cc.noopt.expected
@@ -1,3 +1,8 @@
+class foo {
+public:
+  foo(int x) {}
+};
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -53,11 +58,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-class foo {
-public:
-  foo(int x) {}
-};
-
 int main() { 
   if (!__dredd_enabled_mutation(12)) { new foo[2]{__dredd_replace_expr_int(4, 0), __dredd_replace_expr_int(5, 6)}; } 
 }
diff --git a/test/single_file/printing.c.expected b/test/single_file/printing.c.expected
index 2c7d4bd7..30620849 100644
--- a/test/single_file/printing.c.expected
+++ b/test/single_file/printing.c.expected
@@ -1,3 +1,5 @@
+#include <stdio.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -40,8 +42,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return enabled_bitset[local_mutation_id / 64] & ((uint64_t) 1 << (local_mutation_id % 64));
 }
 
-#include <stdio.h>
-
 int main() {
   if (!__dredd_enabled_mutation(0)) { printf("%s\n", "A\n"); }
   if (!__dredd_enabled_mutation(1)) { printf("%s\n", "B\n"); }
diff --git a/test/single_file/printing.c.noopt.expected b/test/single_file/printing.c.noopt.expected
index bac6e784..d6028964 100644
--- a/test/single_file/printing.c.noopt.expected
+++ b/test/single_file/printing.c.noopt.expected
@@ -1,3 +1,5 @@
+#include <stdio.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -51,8 +53,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <stdio.h>
-
 int main() {
   if (!__dredd_enabled_mutation(6)) { __dredd_replace_expr_int(printf("%s\n", "A\n"), 0); }
   if (!__dredd_enabled_mutation(13)) { __dredd_replace_expr_int(printf("%s\n", "B\n"), 7); }
diff --git a/test/single_file/printing.cc.expected b/test/single_file/printing.cc.expected
index 92acec7c..a030f63d 100644
--- a/test/single_file/printing.cc.expected
+++ b/test/single_file/printing.cc.expected
@@ -1,3 +1,5 @@
+#include <iostream>
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -42,8 +44,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
 }
 
-#include <iostream>
-
 int main() {
   if (!__dredd_enabled_mutation(0)) { std::cout << "A\n"; }
   if (!__dredd_enabled_mutation(1)) { std::cout << "B\n"; }
diff --git a/test/single_file/printing.cc.noopt.expected b/test/single_file/printing.cc.noopt.expected
index 92acec7c..a030f63d 100644
--- a/test/single_file/printing.cc.noopt.expected
+++ b/test/single_file/printing.cc.noopt.expected
@@ -1,3 +1,5 @@
+#include <iostream>
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -42,8 +44,6 @@ static bool __dredd_enabled_mutation(int local_mutation_id) {
   return (enabled_bitset[local_mutation_id / 64] & (static_cast<uint64_t>(1) << (local_mutation_id % 64))) != 0;
 }
 
-#include <iostream>
-
 int main() {
   if (!__dredd_enabled_mutation(0)) { std::cout << "A\n"; }
   if (!__dredd_enabled_mutation(1)) { std::cout << "B\n"; }
diff --git a/test/single_file/sizeof_template2.cc.expected b/test/single_file/sizeof_template2.cc.expected
index fa19d62e..3da4ae70 100644
--- a/test/single_file/sizeof_template2.cc.expected
+++ b/test/single_file/sizeof_template2.cc.expected
@@ -1,3 +1,5 @@
+bool f(int);
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -61,8 +63,6 @@ static bool __dredd_replace_expr_bool(std::function<bool()> arg, int local_mutat
   return arg();
 }
 
-bool f(int);
-
 template <typename a> struct b {
   bool c() { if (!__dredd_enabled_mutation(9)) { return __dredd_replace_expr_bool([&]() -> bool { return static_cast<bool>(f(__dredd_replace_expr_int(sizeof(a), 0))); }, 6); } }
 };
diff --git a/test/single_file/sizeof_template2.cc.noopt.expected b/test/single_file/sizeof_template2.cc.noopt.expected
index e194057e..8e99c8b6 100644
--- a/test/single_file/sizeof_template2.cc.noopt.expected
+++ b/test/single_file/sizeof_template2.cc.noopt.expected
@@ -1,3 +1,5 @@
+bool f(int);
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -70,8 +72,6 @@ static bool __dredd_replace_expr_bool(std::function<bool()> arg, int local_mutat
   return arg();
 }
 
-bool f(int);
-
 template <typename a> struct b {
   bool c() { if (!__dredd_enabled_mutation(13)) { return __dredd_replace_expr_bool([&]() -> bool { return static_cast<bool>(f(__dredd_replace_expr_int(__dredd_replace_expr_unsigned_long(sizeof(a), 0), 4))); }, 10); } }
 };
diff --git a/test/single_file/space_needed_after_macro.c.expected b/test/single_file/space_needed_after_macro.c.expected
index dcfc02eb..05c5072d 100644
--- a/test/single_file/space_needed_after_macro.c.expected
+++ b/test/single_file/space_needed_after_macro.c.expected
@@ -1,3 +1,5 @@
+#define BEGIN x = 
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -51,8 +53,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#define BEGIN x = 
-
 int main() {
   int x, y;
   if (!__dredd_enabled_mutation(6)) { BEGIN __dredd_replace_expr_int((y), 0); }
diff --git a/test/single_file/space_needed_after_macro.c.noopt.expected b/test/single_file/space_needed_after_macro.c.noopt.expected
index c5117c01..80805613 100644
--- a/test/single_file/space_needed_after_macro.c.noopt.expected
+++ b/test/single_file/space_needed_after_macro.c.noopt.expected
@@ -1,3 +1,5 @@
+#define BEGIN x = 
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -58,8 +60,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#define BEGIN x = 
-
 int main() {
   int x, y;
   if (!__dredd_enabled_mutation(14)) { __dredd_replace_expr_int(BEGIN __dredd_replace_expr_int( __dredd_replace_expr_int_lvalue(&((y)), 0), 2), 8); }
diff --git a/test/single_file/space_needed_after_macro2.c.expected b/test/single_file/space_needed_after_macro2.c.expected
index e5e30bf0..ad8d2ebc 100644
--- a/test/single_file/space_needed_after_macro2.c.expected
+++ b/test/single_file/space_needed_after_macro2.c.expected
@@ -1,3 +1,5 @@
+#define BEGIN_ x = 
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -51,8 +53,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#define BEGIN_ x = 
-
 int main() {
   int x, y;
   if (!__dredd_enabled_mutation(6)) { BEGIN_ __dredd_replace_expr_int((y), 0); }
diff --git a/test/single_file/space_needed_after_macro2.c.noopt.expected b/test/single_file/space_needed_after_macro2.c.noopt.expected
index 74125f2a..5848bed4 100644
--- a/test/single_file/space_needed_after_macro2.c.noopt.expected
+++ b/test/single_file/space_needed_after_macro2.c.noopt.expected
@@ -1,3 +1,5 @@
+#define BEGIN_ x = 
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -58,8 +60,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#define BEGIN_ x = 
-
 int main() {
   int x, y;
   if (!__dredd_enabled_mutation(14)) { __dredd_replace_expr_int(BEGIN_ __dredd_replace_expr_int( __dredd_replace_expr_int_lvalue(&((y)), 0), 2), 8); }
diff --git a/test/single_file/switch_cases1.c.expected b/test/single_file/switch_cases1.c.expected
index 8b648e16..055968e1 100644
--- a/test/single_file/switch_cases1.c.expected
+++ b/test/single_file/switch_cases1.c.expected
@@ -1,3 +1,5 @@
+#include <stdio.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -68,8 +70,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <stdio.h>
-
 int main() {
   int x = __dredd_replace_expr_int_constant(10, 0);
   if (!__dredd_enabled_mutation(16)) { switch (__dredd_replace_expr_int(__dredd_replace_expr_int_lvalue(&(x), 5), 7)) {
diff --git a/test/single_file/switch_cases1.c.noopt.expected b/test/single_file/switch_cases1.c.noopt.expected
index 2d2e302d..84e52c84 100644
--- a/test/single_file/switch_cases1.c.noopt.expected
+++ b/test/single_file/switch_cases1.c.noopt.expected
@@ -1,3 +1,5 @@
+#include <stdio.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -58,8 +60,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <stdio.h>
-
 int main() {
   int x = __dredd_replace_expr_int(10, 0);
   if (!__dredd_enabled_mutation(35)) { switch (__dredd_replace_expr_int(__dredd_replace_expr_int_lvalue(&(x), 6), 8)) {
diff --git a/test/single_file/switch_cases2.c.expected b/test/single_file/switch_cases2.c.expected
index 2af0ea6d..d5a08601 100644
--- a/test/single_file/switch_cases2.c.expected
+++ b/test/single_file/switch_cases2.c.expected
@@ -1,3 +1,5 @@
+#include <stdio.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -68,8 +70,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <stdio.h>
-
 int main() {
   int x = __dredd_replace_expr_int_constant(10, 0);
   if (!__dredd_enabled_mutation(16)) { switch (__dredd_replace_expr_int(__dredd_replace_expr_int_lvalue(&(x), 5), 7)) {
diff --git a/test/single_file/switch_cases2.c.noopt.expected b/test/single_file/switch_cases2.c.noopt.expected
index b461a13e..14f0be4c 100644
--- a/test/single_file/switch_cases2.c.noopt.expected
+++ b/test/single_file/switch_cases2.c.noopt.expected
@@ -1,3 +1,5 @@
+#include <stdio.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -58,8 +60,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <stdio.h>
-
 int main() {
   int x = __dredd_replace_expr_int(10, 0);
   if (!__dredd_enabled_mutation(35)) { switch (__dredd_replace_expr_int(__dredd_replace_expr_int_lvalue(&(x), 6), 8)) {
diff --git a/test/single_file/typedef.c.noopt.expected b/test/single_file/typedef.c.noopt.expected
index 92df5b23..1a054a9a 100644
--- a/test/single_file/typedef.c.noopt.expected
+++ b/test/single_file/typedef.c.noopt.expected
@@ -1,3 +1,7 @@
+typedef struct S {
+  int x;
+} SomeS;
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -62,10 +66,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int(int arg1, int a
   return arg1 + arg2;
 }
 
-typedef struct S {
-  int x;
-} SomeS;
-
 void foo() {
   if (!__dredd_enabled_mutation(24)) { __dredd_replace_expr_int(__dredd_replace_binary_operator_Add_arg1_int_arg2_int(__dredd_replace_expr_int(1, 0) , __dredd_replace_expr_int(2, 6), 12), 18); }
 }
diff --git a/test/single_file/typedef.cc.noopt.expected b/test/single_file/typedef.cc.noopt.expected
index 9b7ac517..6f5b2381 100644
--- a/test/single_file/typedef.cc.noopt.expected
+++ b/test/single_file/typedef.cc.noopt.expected
@@ -1,3 +1,7 @@
+typedef struct S {
+  int x;
+} SomeS;
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -64,10 +68,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int(int arg1, int a
   return arg1 + arg2;
 }
 
-typedef struct S {
-  int x;
-} SomeS;
-
 void foo() {
   if (!__dredd_enabled_mutation(24)) { __dredd_replace_expr_int(__dredd_replace_binary_operator_Add_arg1_int_arg2_int(__dredd_replace_expr_int(1, 0) , __dredd_replace_expr_int(2, 6), 12), 18); }
 }
diff --git a/test/single_file/unary_logical_not.c.expected b/test/single_file/unary_logical_not.c.expected
index 39208349..49e39509 100644
--- a/test/single_file/unary_logical_not.c.expected
+++ b/test/single_file/unary_logical_not.c.expected
@@ -1,3 +1,5 @@
+#include <stdbool.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -72,8 +74,6 @@ static bool __dredd_replace_expr_bool(bool arg, int local_mutation_id) {
   return arg;
 }
 
-#include <stdbool.h>
-
 int main() {
   bool y = __dredd_replace_expr_bool_true(true, 0);
   if (!__dredd_enabled_mutation(12)) { return __dredd_replace_expr_int(__dredd_replace_unary_operator_LNot_bool(__dredd_replace_expr_bool(y, 1), 4), 6); }
diff --git a/test/single_file/unary_logical_not.c.noopt.expected b/test/single_file/unary_logical_not.c.noopt.expected
index 6c35a295..2e97e9a8 100644
--- a/test/single_file/unary_logical_not.c.noopt.expected
+++ b/test/single_file/unary_logical_not.c.noopt.expected
@@ -1,3 +1,5 @@
+#include <stdbool.h>
+
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -67,8 +69,6 @@ static bool __dredd_replace_expr_bool(bool arg, int local_mutation_id) {
   return arg;
 }
 
-#include <stdbool.h>
-
 int main() {
   bool y = __dredd_replace_expr_bool(__dredd_replace_expr_int(true, 0), 6);
   if (!__dredd_enabled_mutation(21)) { return __dredd_replace_expr_int(__dredd_replace_unary_operator_LNot_bool(__dredd_replace_expr_bool(y, 9), 12), 15); }
diff --git a/test/single_file/user_defined_literals.cc.expected b/test/single_file/user_defined_literals.cc.expected
index be6c6216..b45be2fe 100644
--- a/test/single_file/user_defined_literals.cc.expected
+++ b/test/single_file/user_defined_literals.cc.expected
@@ -1,3 +1,6 @@
+#include <cstdint>
+
+// Number wraps integer, enforcing explicit casting
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -74,9 +77,6 @@ static int __dredd_replace_expr_int_zero(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <cstdint>
-
-// Number wraps integer, enforcing explicit casting
 struct Number {
     
     uint32_t value = {};
diff --git a/test/single_file/user_defined_literals.cc.noopt.expected b/test/single_file/user_defined_literals.cc.noopt.expected
index 42755449..f6a9e269 100644
--- a/test/single_file/user_defined_literals.cc.noopt.expected
+++ b/test/single_file/user_defined_literals.cc.noopt.expected
@@ -1,3 +1,6 @@
+#include <cstdint>
+
+// Number wraps integer, enforcing explicit casting
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -78,9 +81,6 @@ static int __dredd_replace_expr_int(int arg, int local_mutation_id) {
   return arg;
 }
 
-#include <cstdint>
-
-// Number wraps integer, enforcing explicit casting
 struct Number {
     
     uint32_t value = {};
diff --git a/test/single_file/using.cc.noopt.expected b/test/single_file/using.cc.noopt.expected
index 5eb65996..c46f76c7 100644
--- a/test/single_file/using.cc.noopt.expected
+++ b/test/single_file/using.cc.noopt.expected
@@ -1,3 +1,5 @@
+using blah = int;
+
 #include <cinttypes>
 #include <cstddef>
 #include <functional>
@@ -64,8 +66,6 @@ static int __dredd_replace_binary_operator_Add_arg1_int_arg2_int(int arg1, int a
   return arg1 + arg2;
 }
 
-using blah = int;
-
 void foo() {
   if (!__dredd_enabled_mutation(24)) { __dredd_replace_expr_int(__dredd_replace_binary_operator_Add_arg1_int_arg2_int(__dredd_replace_expr_int(1, 0) , __dredd_replace_expr_int(2, 6), 12), 18); }
 }