diff --git a/aiocoap/resource.py b/aiocoap/resource.py
index 25a19689..ee9080c8 100644
--- a/aiocoap/resource.py
+++ b/aiocoap/resource.py
@@ -174,7 +174,7 @@ def updated_state(self, response=None):
         should be sent to observers."""
 
         for o in self._observations:
-            o.trigger(response)
+            o.trigger(response.copy() if response else response)
 
     def get_link_description(self):
         link = super(ObservableResource, self).get_link_description()