diff --git a/lib/compress.js b/lib/compress.js
index 74e09299b2..1e358599f5 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1378,6 +1378,7 @@ Compressor.prototype.compress = function(node) {
         def(AST_LambdaDefinition, function(tw, descend, compressor) {
             var fn = this;
             var def = fn.name.definition();
+            if (!safe_to_trim(fn)) def.fixed = false;
             var parent = tw.parent();
             if (parent instanceof AST_ExportDeclaration || parent instanceof AST_ExportDefault) def.single_use = false;
             if (!safe_to_visit(tw, fn)) return true;
@@ -3545,17 +3546,10 @@ Compressor.prototype.compress = function(node) {
                     if (node instanceof AST_Symbol) {
                         var def = node.definition();
                         var scope = def.scope.resolve();
-                        var found = false;
-                        var avoid = def.orig.reduce(function(scopes, sym) {
+                        def.orig.forEach(function(sym) {
                             if (sym instanceof AST_SymbolDefun) {
                                 if (sym.scope !== scope) push_uniq(scopes, sym.scope);
-                            } else {
-                                found = true;
                             }
-                            return scopes;
-                        }, []);
-                        if (found) avoid.forEach(function(scope) {
-                            push_uniq(scopes, scope);
                         });
                     }
                 });
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index df6e113492..f1f4d61188 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -10357,3 +10357,81 @@ issue_5869: {
     }
     expect_stdout: TypeError("Cannot set properties of undefined")
 }
+
+issue_5915_1: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        f = void 0;
+        {
+            console.log(typeof f);
+            function f() {}
+        }
+    }
+    expect: {
+        f = void 0;
+        {
+            console.log(typeof f);
+            function f() {}
+        }
+    }
+    expect_stdout: true
+}
+
+issue_5915_2: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        f = void 0;
+        {
+            function f() {}
+            console.log(typeof f);
+        }
+    }
+    expect: {
+        f = void 0;
+        {
+            function f() {}
+            console.log(typeof f);
+        }
+    }
+    expect_stdout: true
+}
+
+issue_5915_3: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        f = void 0;
+        function f() {}
+        {
+            console.log(typeof f);
+        }
+    }
+    expect: {
+        function f() {}
+        console.log(typeof (f = void 0));
+    }
+    expect_stdout: "undefined"
+}
+
+issue_5915_4: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        {
+            f = void 0;
+            function f() {}
+            console.log(typeof f);
+        }
+    }
+    expect: {
+        function f() {}
+        console.log(typeof (f = void 0));
+    }
+    expect_stdout: "undefined"
+}
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index edd95bd009..8108f18d10 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -8493,3 +8493,96 @@ issue_5892: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5915_1: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        f = void 0;
+        if (console) {
+            console.log(typeof f);
+            function f() {}
+        }
+    }
+    expect: {
+        f = void 0;
+        if (console) {
+            console.log(typeof f);
+            function f() {}
+        }
+    }
+    expect_stdout: true
+}
+
+issue_5915_2: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        f = void 0;
+        if (console) {
+            function f() {}
+            console.log(typeof f);
+        }
+    }
+    expect: {
+        f = void 0;
+        if (console) {
+            function f() {}
+            console.log(typeof f);
+        }
+    }
+    expect_stdout: true
+}
+
+issue_5915_3: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        f = void 0;
+        function f() {}
+        if (console) {
+            console.log(typeof f);
+        }
+    }
+    expect: {
+        void 0;
+        if (console)
+            console.log("undefined");
+    }
+    expect_stdout: "undefined"
+}
+
+issue_5915_4: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        if (console) {
+            f = void 0;
+            function f() {}
+            console.log(typeof f);
+        }
+    }
+    expect: {
+        if (console) {
+            void 0;
+            console.log("undefined");
+        }
+    }
+    expect_stdout: "undefined"
+}