diff --git a/pkg/dart2wasm/lib/record_class_generator.dart b/pkg/dart2wasm/lib/record_class_generator.dart
index e5f6c4a2dd6..4c9ada35b01 100644
--- a/pkg/dart2wasm/lib/record_class_generator.dart
+++ b/pkg/dart2wasm/lib/record_class_generator.dart
@@ -395,7 +395,8 @@ class _RecordClassGenerator {
         Procedure(
           Name('toString', library),
           ProcedureKind.Method,
-          FunctionNode(ReturnStatement(stringExpression)),
+          FunctionNode(ReturnStatement(stringExpression),
+              returnType: coreTypes.stringNonNullableRawType),
           fileUri: library.fileUri,
         ),
         coreTypes);