diff --git a/trytond/cache.py b/trytond/cache.py
index 07a9bed258..ae1fc3381a 100644
--- a/trytond/cache.py
+++ b/trytond/cache.py
@@ -83,7 +83,7 @@ class BaseCache(object):
 
     def _key(self, key):
         if self.context:
-            context = Transaction().context
+            context = Transaction().context.copy()
             context.pop('client', None)
             return (key, Transaction().user, freeze(context))
         return key