diff --git a/product/ERP5Type/Utils.py b/product/ERP5Type/Utils.py
index 7445cd4601a034b6506bba12b507c27a7052580f..18985307b76af09fe03e78aceb601af17a7fc940 100755
--- a/product/ERP5Type/Utils.py
+++ b/product/ERP5Type/Utils.py
@@ -96,12 +96,13 @@ def cartesianProduct(list_of_list):
   if len(list_of_list) == 0:
     return [[]]
   result = []
+  append = result.append
   head = list_of_list[0]
   tail = list_of_list[1:]
   product = cartesianProduct(tail)
   for v in head:
     for p in product:
-      result += [[v] + p]
+      append([v] + p)
   return result
 
 # Some list operations