diff --git a/packages/flutter/test/foundation/isolates_test.dart b/packages/flutter/test/foundation/isolates_test.dart
index 24b834bc0c..eead4e2e2d 100644
--- a/packages/flutter/test/foundation/isolates_test.dart
+++ b/packages/flutter/test/foundation/isolates_test.dart
@@ -89,9 +89,8 @@ Future<void> expectFileSuccessfullyCompletes(String filename) async {
   final String flutterRoot = platform.environment['FLUTTER_ROOT']!;
   final String dartPath =
       fs.path.join(flutterRoot, 'bin', 'cache', 'dart-sdk', 'bin', 'dart');
-  final String packageRoot = fs.path.dirname(fs.path.fromUri(platform.script));
   final String scriptPath =
-      fs.path.join(packageRoot, 'test', 'foundation', filename);
+      fs.path.join(flutterRoot, 'packages', 'flutter', 'test', 'foundation', filename);
 
   // Enable asserts to also catch potentially invalid assertions.
   final ProcessResult result = await Process.run(