diff --git a/artiq/devices/ctlmgr.py b/artiq/devices/ctlmgr.py
index 52f203545..93306df6d 100644
--- a/artiq/devices/ctlmgr.py
+++ b/artiq/devices/ctlmgr.py
@@ -180,7 +180,8 @@ class Controllers:
     def __setitem__(self, k, v):
         try:
             if (isinstance(v, dict) and v["type"] == "controller" and
-                    self.host_filter in get_ip_addresses(v["host"])):
+                    self.host_filter in get_ip_addresses(v["host"]) and
+                    "command" in v):
                 v["command"] = v["command"].format(name=k,
                                                    bind=self.host_filter,
                                                    port=v["port"])