diff --git a/masque/ports.py b/masque/ports.py
index 6179f87..b1943a3 100644
--- a/masque/ports.py
+++ b/masque/ports.py
@@ -1,4 +1,4 @@
-from typing import Iterable, KeysView, ValuesView, overload, Self, Mapping
+from typing import Iterable, KeysView, ValuesView, overload, Self, Mapping, NoReturn
 import warnings
 import traceback
 import logging
@@ -138,6 +138,9 @@ class PortList(metaclass=ABCMeta):
         else:
             return {k: self.ports[k] for k in key}
 
+    def __contains__(self, key: str) -> NoReturn:
+        raise NotImplementedError('PortsList.__contains__ is left unimplemented. Use `key in container.ports` instead.')
+
     # NOTE: Didn't add keys(), items(), values(), __contains__(), etc.
     # because it's weird on stuff like Pattern that contains other lists
     # and because you can just grab .ports and use that instead