diff --git a/src/CacheResponse.php b/src/CacheResponse.php
index efc26b3..71d3309 100644
--- a/src/CacheResponse.php
+++ b/src/CacheResponse.php
@@ -34,7 +34,7 @@ public function for(string $time)
         $this->response->setSharedMaxAge($seconds);
     }
 
-    public function isWebResponse()
+    public function isWebResponse(): bool
     {
         return $this->response instanceof \craft\web\Response;
     }