diff --git a/common/web/langtags/src/main.ts b/common/web/langtags/src/main.ts
index 44c0a69041..410bae313a 100644
--- a/common/web/langtags/src/main.ts
+++ b/common/web/langtags/src/main.ts
@@ -114,7 +114,7 @@ function preinit(): void {
  * @returns LangTag or undefined if not found
  */
 function getLangtagByTag(tag: string): LangTag {
-  return langtagsByTag.get(tag.toLowerCase());
+  return langtagsByTag.get(tag?.toLowerCase());
 }
 
 preinit();