diff --git a/compiler/src/dmd/globals.d b/compiler/src/dmd/globals.d
index 901561fcf8e..7fd3fc3ef59 100644
--- a/compiler/src/dmd/globals.d
+++ b/compiler/src/dmd/globals.d
@@ -198,7 +198,7 @@ extern (C++) struct Param
     FeatureState safer;          // safer by default (more @safe checks in unattributed code)
                                  // https://github.com/WalterBright/documents/blob/38f0a846726b571f8108f6e63e5e217b91421c86/safer.md
     FeatureState noSharedAccess; // read/write access to shared memory objects
-    bool previewIn;              // `in` means `[ref] scope const`, accepts rvalues
+    bool previewIn = true;       // `in` means `[ref] scope const`, accepts rvalues
     bool inclusiveInContracts;   // 'in' contracts of overridden methods must be a superset of parent contract
     bool shortenedMethods = true;       // allow => in normal function declarations
     bool fixImmutableConv;       // error on unsound immutable conversion - https://github.com/dlang/dmd/pull/14070
diff --git a/compiler/test/compilable/testfptr.d b/compiler/test/compilable/testfptr.d
index e6a0dd670df..d9a375c69c6 100644
--- a/compiler/test/compilable/testfptr.d
+++ b/compiler/test/compilable/testfptr.d
@@ -107,17 +107,12 @@ void bug3797()
     static assert(!is(typeof( purefunc = nonpurefunc )));
     static assert( is(typeof( nonpurefunc = purefunc )));
 
-    // Cannot convert parameter storage classes (except const to in and in to const)
-
-    void function(const(int)) constfunc;
+    // Cannot convert parameter storage classes
     void function(in int) infunc;
     void function(out int) outfunc;
     void function(ref int) reffunc;
     void function(lazy int) lazyfunc;
 
-    static assert(is(typeof( infunc = constfunc )));
-    static assert(is(typeof( constfunc = infunc )));
-
     static assert(!is(typeof( infunc = outfunc )));
     static assert(!is(typeof( infunc = reffunc )));
     static assert(!is(typeof( infunc = lazyfunc )));
@@ -250,17 +245,12 @@ void bug3797dg()
     static assert(!is(typeof( purefunc = nonpurefunc )));
     static assert( is(typeof( nonpurefunc = purefunc )));
 
-    // Cannot convert parameter storage classes (except const to in and in to const)
-
-    void delegate(const(int)) constfunc;
+    // Cannot convert parameter storage classes
     void delegate(in int) infunc;
     void delegate(out int) outfunc;
     void delegate(ref int) reffunc;
     void delegate(lazy int) lazyfunc;
 
-    static assert(is(typeof( infunc = constfunc )));
-    static assert(is(typeof( constfunc = infunc )));
-
     static assert(!is(typeof( infunc = outfunc )));
     static assert(!is(typeof( infunc = reffunc )));
     static assert(!is(typeof( infunc = lazyfunc )));
diff --git a/compiler/test/fail_compilation/deprecations_preview_in.d b/compiler/test/fail_compilation/deprecations_preview_in.d
index 33cc904e4be..ed7d7d348e3 100644
--- a/compiler/test/fail_compilation/deprecations_preview_in.d
+++ b/compiler/test/fail_compilation/deprecations_preview_in.d
@@ -2,7 +2,7 @@
 REQUIRED_ARGS: -de
 TEST_OUTPUT:
 ---
-fail_compilation/deprecations_preview_in.d(1): Deprecation: using `in` parameters with `extern(C)` functions is deprecated
+fail_compilation/deprecations_preview_in.d(1): Error: cannot use `in` parameters with `extern(C)` functions
 fail_compilation/deprecations_preview_in.d(1):        parameter `__anonymous_param` declared as `in` here
 ---
 */
diff --git a/compiler/test/fail_compilation/fail183.d b/compiler/test/fail_compilation/fail183.d
index 362213c1f64..b086893bf41 100644
--- a/compiler/test/fail_compilation/fail183.d
+++ b/compiler/test/fail_compilation/fail183.d
@@ -2,13 +2,13 @@
 TEST_OUTPUT:
 ---
 fail_compilation/fail183.d(17): Error: attribute `const` is redundant with previously-applied `in`
-fail_compilation/fail183.d(18): Error: attribute `scope` cannot be applied with `in`, use `-preview=in` instead
+fail_compilation/fail183.d(18): Error: attribute `scope` is redundant with previously-applied `in`
 fail_compilation/fail183.d(19): Error: attribute `const` is redundant with previously-applied `in`
-fail_compilation/fail183.d(19): Error: attribute `scope` cannot be applied with `in`, use `-preview=in` instead
-fail_compilation/fail183.d(20): Error: attribute `scope` cannot be applied with `in`, use `-preview=in` instead
+fail_compilation/fail183.d(19): Error: attribute `scope` is redundant with previously-applied `in`
+fail_compilation/fail183.d(20): Error: attribute `scope` is redundant with previously-applied `in`
 fail_compilation/fail183.d(20): Error: attribute `const` is redundant with previously-applied `in`
 fail_compilation/fail183.d(22): Error: attribute `in` cannot be added after `const`: remove `const`
-fail_compilation/fail183.d(23): Error: attribute `in` cannot be added after `scope`: remove `scope` and use `-preview=in`
+fail_compilation/fail183.d(23): Error: attribute `in` cannot be added after `scope`: remove `scope`
 fail_compilation/fail183.d(24): Error: attribute `in` cannot be added after `const`: remove `const`
 fail_compilation/fail183.d(25): Error: attribute `in` cannot be added after `const`: remove `const`
 ---
diff --git a/compiler/test/run.d b/compiler/test/run.d
index efc5e3d9df2..655df2b3b99 100755
--- a/compiler/test/run.d
+++ b/compiler/test/run.d
@@ -163,7 +163,7 @@ Options:
         args = ["all"];
 
     // move any long-running tests to the front
-    static size_t sortKey(in ref Target target)
+    static size_t sortKey(const scope ref Target target)
     {
         const name = target.normalizedTestName;
         if (name.startsWith("runnable"))