diff --git a/zuul/scheduler.py b/zuul/scheduler.py
index 57ee5710d7..d62709e1dd 100644
--- a/zuul/scheduler.py
+++ b/zuul/scheduler.py
@@ -351,6 +351,7 @@ class Scheduler(threading.Thread):
         self.rpc.join()
         self._command_running = False
         self.command_socket.stop()
+        self.command_thread.join()
 
     def runCommand(self):
         while self._command_running: