diff --git a/system/src/Grav/Common/Page/Page.php b/system/src/Grav/Common/Page/Page.php
index <HASH>..<HASH> 100644
--- a/system/src/Grav/Common/Page/Page.php
+++ b/system/src/Grav/Common/Page/Page.php
@@ -1207,7 +1207,7 @@ class Page implements PageInterface
     /**
      * @return string
      */
-    protected function getCacheKey()
+    protected function getCacheKey(): string
     {
         return $this->id();
     }
One more PHP <I> issue