diff --git a/katcp/sensortree.py b/katcp/sensortree.py
index <HASH>..<HASH> 100644
--- a/katcp/sensortree.py
+++ b/katcp/sensortree.py
@@ -50,7 +50,7 @@ class GenericSensorTree(object):
         sensor : :class:`katcp.Sensor`
             The sensor whose value has changed.
         """
-        parents = self._child_to_parents[sensor]
+        parents = list(self._child_to_parents[sensor])
         for parent in parents:
             self.recalculate(parent, (sensor,))
Handle addition of new sensors to the sensor tree during a sensor update without crashing (missing part from last commit).

git-svn-id: <URL>