diff --git a/src/Adapter/AbstractAdapter.php b/src/Adapter/AbstractAdapter.php
index e577ac4a7..a6a8ed026 100644
--- a/src/Adapter/AbstractAdapter.php
+++ b/src/Adapter/AbstractAdapter.php
@@ -67,6 +67,6 @@ public function applyPathPrefix($path)
      */
     public function removePathPrefix($path)
     {
-        return substr($path, strlen($this->getPathPrefix()));
+        return substr($path, strlen((string) $this->getPathPrefix()));
     }
 }