diff --git a/src/auth/loginticket.ts b/src/auth/loginticket.ts
index 1a86d2ca..ab4208bf 100644
--- a/src/auth/loginticket.ts
+++ b/src/auth/loginticket.ts
@@ -179,4 +179,10 @@ export interface TokenPayload {
    * a hosted domain.
    */
   hd?: string;
+
+  /**
+   * The user's locale, represented by a BCP 47 language tag.
+   * Might be provided when a name claim is present.
+   */
+  locale?: string;
 }