diff --git a/react-router-redux/index.d.ts b/react-router-redux/index.d.ts
index b37af67b2f..16438f9452 100644
--- a/react-router-redux/index.d.ts
+++ b/react-router-redux/index.d.ts
@@ -59,7 +59,7 @@ declare namespace ReactRouterRedux {
         locationBeforeTransitions: History.Location
     }
 
-    function routerReducer(state?: RouterState, options?: any): R.Reducer<RouterState>
+    function routerReducer(state?: RouterState, action?: R.Action): RouterState;
     function syncHistoryWithStore(history: History.History, store: R.Store<any>, options?: SyncHistoryWithStoreOptions): ReactRouterReduxHistory;
     function routerMiddleware(history: History.History): R.Middleware;
 }