diff --git a/lib/Garbagecollector.class.php b/lib/Garbagecollector.class.php
index 0075505..c1be691 100644
--- a/lib/Garbagecollector.class.php
+++ b/lib/Garbagecollector.class.php
@@ -82,6 +82,11 @@ protected function filterVersions(array &$outdated_files)
             {
                 continue;
             }
+		
+            if (!isset($m['group']))
+            {
+                continue;
+            }
 
             if (!isset($groups[ $m['group'] ]))
             {