diff --git a/beets/library.py b/beets/library.py
index 64b7d5b7a..7b9be58d6 100644
--- a/beets/library.py
+++ b/beets/library.py
@@ -138,11 +138,13 @@ class Item(object):
             store_id = self.id
  
         # build assignments for query
-        assignments = ','.join( ['?=?'] * (len(item_fields)-1) )
+        assignments = ''
         subvars = []
         for key in item_keys:
             if key != 'id':
-                subvars += [key, self.record[key]]
+                assignments += key + '=?,'
+                subvars.append(self.record[key])
+        assignments = assignments[:-1] # knock off last ,
 
         # finish the query
         query = 'update items set ' + assignments + ' where id=?'