diff --git a/tools/public_api_guard/platform-browser/platform-browser.d.ts b/tools/public_api_guard/platform-browser/platform-browser.d.ts
index 5c55225bd9..5eaa48d089 100644
--- a/tools/public_api_guard/platform-browser/platform-browser.d.ts
+++ b/tools/public_api_guard/platform-browser/platform-browser.d.ts
@@ -60,7 +60,7 @@ export declare class HammerGestureConfig {
 }
 
 /** @experimental */
-export declare function makeStateKey<T =
+export declare function makeStateKey<T = void>(key: string): StateKey<T>;
 
 /** @experimental */
 export declare class Meta {