diff --git a/product/ERP5Type/XMLMatrix.py b/product/ERP5Type/XMLMatrix.py
index 1bdf46385111eb26a698f7e855997f8ae5f502ac..89fb1ddba3fc3f1e146d5e315c3b22aa3675d571 100644
--- a/product/ERP5Type/XMLMatrix.py
+++ b/product/ERP5Type/XMLMatrix.py
@@ -479,8 +479,7 @@ class XMLMatrix(Folder):
       result = []
       for value in cell_range.itervalues():
         result_items = sorted(value.iteritems(), key=lambda x:x[1])
-        result_items = [x[0] for x in result_items]
-        result += [result_items]
+        result.extend(x[0] for x in result_items)
       return result
 
     security.declareProtected( Permissions.ModifyPortalContent, 'newCell' )