diff --git a/classes/Avatar.php b/classes/Avatar.php
index 62885f402b..516abafe25 100644
--- a/classes/Avatar.php
+++ b/classes/Avatar.php
@@ -207,8 +207,11 @@ class Avatar extends Managed_DataObject
         }
     }
 
-    static function defaultImage($size=AVATAR_PROFILE_SIZE)
+    static function defaultImage($size=null)
     {
+        if (is_null($size)) {
+            $size = AVATAR_PROFILE_SIZE;
+        }
         static $sizenames = array(AVATAR_PROFILE_SIZE => 'profile',
                                   AVATAR_STREAM_SIZE => 'stream',
                                   AVATAR_MINI_SIZE => 'mini');