diff --git a/pkgs/test_core/CHANGELOG.md b/pkgs/test_core/CHANGELOG.md
index 6110d421f..f5fd8899b 100644
--- a/pkgs/test_core/CHANGELOG.md
+++ b/pkgs/test_core/CHANGELOG.md
@@ -1,6 +1,7 @@
 ## 0.6.5-wip
 
 * Increase SDK constraint to ^3.4.0.
+* Ensure we don't create files ending in a `.`, this breaks windows.
 
 ## 0.6.4
 
diff --git a/pkgs/test_core/lib/src/runner/package_version.dart b/pkgs/test_core/lib/src/runner/package_version.dart
index 5f4d622d3..0ce77d371 100644
--- a/pkgs/test_core/lib/src/runner/package_version.dart
+++ b/pkgs/test_core/lib/src/runner/package_version.dart
@@ -18,6 +18,6 @@ Future<String> get rootPackageLanguageVersionComment =>
 final _rootPackageLanguageVersionComment = DetachingFuture(() async {
   var packageConfig = await loadPackageConfigUri(await packageConfigUri);
   var rootPackage = packageConfig.packageOf(Uri.file(p.absolute('foo.dart')));
-  if (rootPackage == null) return '';
+  if (rootPackage == null) return '// <unknown-language-version>';
   return '// @dart=${rootPackage.languageVersion}';
 }());