Index: update-mime-database.c
===================================================================
--- update-mime-database.c	(revision 16170)
+++ update-mime-database.c	(working copy)
@@ -2220,7 +2220,10 @@ write_match (gpointer key,
       return;
     }
 
+  if (magic->matches)
     offset = mdata->offset + 32 * g_list_index (mdata->matches, magic->matches->data);
+  else
+    offset = 0;
 
   if (!write_card32 (mdata->cache, offset))
     {