diff --git a/plugins/RedisCache/RedisCachePlugin.php b/plugins/RedisCache/RedisCachePlugin.php
index e15150c4c9..62c5b09c43 100644
--- a/plugins/RedisCache/RedisCachePlugin.php
+++ b/plugins/RedisCache/RedisCachePlugin.php
@@ -115,7 +115,7 @@ class RedisCachePlugin extends Plugin
         }
 
         // Let other caches delete stuff if we didn't succeed
-        return $ret === 1;
+        return isset($ret) && $ret === 1;
     }
 
     function onStartCacheIncrement(&$key, &$step, &$value)