diff --git a/pkg/dev_compiler/lib/src/kernel/compiler.dart b/pkg/dev_compiler/lib/src/kernel/compiler.dart
index 23cc2bae20c..0801c1cd03e 100644
--- a/pkg/dev_compiler/lib/src/kernel/compiler.dart
+++ b/pkg/dev_compiler/lib/src/kernel/compiler.dart
@@ -3239,7 +3239,8 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
 
       if (_annotatedNullCheck(p.annotations)) {
         body.add(_nullParameterCheck(jsParam));
-      } else if (_mustBeNonNullable(p.type) &&
+      } else if (!_options.soundNullSafety &&
+          _mustBeNonNullable(p.type) &&
           !_annotatedNotNull(p.annotations)) {
         // TODO(vsm): Remove if / when CFE does this:
         // https://github.com/dart-lang/sdk/issues/40597
diff --git a/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart b/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart
index 0a3c9a25350..6b33186ead6 100644
--- a/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart
+++ b/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart
@@ -25,22 +25,21 @@ assertFailed(String? message,
 }
 
 final _nullFailedSet = JS('!', 'new Set()');
+
+String _nullFailedMessage(variableName) =>
+    'A null value was passed into a non-nullable parameter: $variableName.';
+
 // Run-time null safety assertion per:
 // https://github.com/dart-lang/language/blob/master/accepted/future-releases/nnbd/feature-specification.md#automatic-debug-assertion-insertion
 nullFailed(String? fileUri, int? line, int? column, String? variable) {
   if (_nonNullAsserts) {
-    throw AssertionErrorImpl(
-        'A null value was passed into a non-nullable parameter $variable',
-        fileUri,
-        line,
-        column,
-        '$variable != null');
+    throw AssertionErrorImpl(_nullFailedMessage(variable), fileUri, line,
+        column, '$variable != null');
   }
   var key = '$fileUri:$line:$column';
   if (!JS('!', '#.has(#)', _nullFailedSet, key)) {
     JS('', '#.add(#)', _nullFailedSet, key);
-    _nullWarn(
-        'A null value was passed into a non-nullable parameter $variable');
+    _nullWarn(_nullFailedMessage(variable));
   }
 }