diff --git a/nodepool/driver/statemachine.py b/nodepool/driver/statemachine.py
index c18509665..243fae604 100644
--- a/nodepool/driver/statemachine.py
+++ b/nodepool/driver/statemachine.py
@@ -291,7 +291,8 @@ class StateMachineNodeLauncher(stats.StatsReporter):
             if state_machine.state != old_state:
                 self.log.debug("State machine for %s advanced from %s to %s",
                                node.id, old_state, state_machine.state)
-            if not node.external_id and state_machine.external_id:
+            if (state_machine.external_id and
+                node.external_id != state_machine.external_id):
                 node.external_id = state_machine.external_id
                 self.zk.storeNode(node)
             if state_machine.complete and not self.nodescan_request: