diff --git a/library/HTMLPurifier/DefinitionCache/Null.php b/library/HTMLPurifier/DefinitionCache/Null.php
index 0f106515..559fc9ba 100644
--- a/library/HTMLPurifier/DefinitionCache/Null.php
+++ b/library/HTMLPurifier/DefinitionCache/Null.php
@@ -24,7 +24,7 @@ class HTMLPurifier_DefinitionCache_Null extends HTMLPurifier_DefinitionCache
         return false;
     }
     
-    function flush() {
+    function flush($config) {
         return false;
     }