diff --git a/purchase.py b/purchase.py
index dfc8f1b94a..57d1faced2 100644
--- a/purchase.py
+++ b/purchase.py
@@ -1836,7 +1836,7 @@ class Move(ModelSQL, ModelView):
         return res
 
     def search_purchase(self, name, clause):
-        return [('purchase_line.' + name,) + clause[1:]]
+        return [('purchase_line.' + name,) + tuple(clause[1:])]
 
     def get_purchase_fields(self, ids, names):
         res = {}
@@ -1887,7 +1887,7 @@ class Move(ModelSQL, ModelView):
         return res
 
     def search_supplier(self, name, clause):
-        return [('purchase_line.purchase.party',) + clause[1:]]
+        return [('purchase_line.purchase.party',) + tuple(clause[1:])]
 
     def write(self, ids, vals):
         purchase_obj = Pool().get('purchase.purchase')