diff --git a/lib/ui/window.dart b/lib/ui/window.dart
index f9bb67ed29bee..4a012d7b0949a 100644
--- a/lib/ui/window.dart
+++ b/lib/ui/window.dart
@@ -395,7 +395,6 @@ class Locale {
   ///
   /// The format of the produced string is 'language-script_country'. Any null field
   /// will result in the corresponding encoding being omitted.
-  @override
   String toCompleteString() {
     final StringBuffer out = StringBuffer(languageCode);
     if (scriptCode != null)
diff --git a/testing/dart/locale_test.dart b/testing/dart/locale_test.dart
index 66fd537a72444..00858a5e81b27 100644
--- a/testing/dart/locale_test.dart
+++ b/testing/dart/locale_test.dart
@@ -27,7 +27,10 @@ void main() {
 
     expect(const Locale.fromSubtags(languageCode: 'en').toString(), 'en');
     expect(const Locale.fromSubtags(languageCode: 'en').languageCode, 'en');
-    expect(const Locale.fromSubtags(scriptCode: 'Latn').toString(), 'und_Latn');
+    expect(const Locale.fromSubtags(scriptCode: 'Latn').toString(), 'und');
+    expect(const Locale.fromSubtags(scriptCode: 'Latn').toCompleteString(), 'und-Latn');
+    expect(const Locale.fromSubtags(scriptCode: 'Latn', countryCode: 'US').toCompleteString(), 'und_US');
+    expect(const Locale.fromSubtags(scriptCode: 'Latn', countryCode: 'US').toCompleteString(), 'und-Latn_US');
     expect(const Locale.fromSubtags(scriptCode: 'Latn').scriptCode, 'Latn');
     expect(const Locale.fromSubtags(countryCode: 'US').toString(), 'und_US');
     expect(const Locale.fromSubtags(countryCode: 'US').countryCode, 'US');