diff --git a/masque/builder/builder.py b/masque/builder/builder.py
index b8b00be..fed839a 100644
--- a/masque/builder/builder.py
+++ b/masque/builder/builder.py
@@ -2,7 +2,7 @@
 Simplified Pattern assembly (`Builder`)
 """
 from typing import Self
-from collections.abc import Sequence, Mapping
+from collections.abc import Iterable, Sequence, Mapping
 import copy
 import logging
 from functools import wraps
diff --git a/masque/ports.py b/masque/ports.py
index e85b2d9..1cc711a 100644
--- a/masque/ports.py
+++ b/masque/ports.py
@@ -515,7 +515,7 @@ class PortList(metaclass=ABCMeta):
             o_offsets[:, 1] *= -1
             o_rotations *= -1
 
-        ok_pairs = {tuple(sorted(pair)) for pair in ok_connections if pair[0] != pair[1])}
+        ok_pairs = {tuple(sorted(pair)) for pair in ok_connections if pair[0] != pair[1]}
         type_conflicts = numpy.array([(st != ot) and ('unk' not in (st, ot)) and (tuple(sorted((st, ot))) not in ok_pairs)
                                       for st, ot in zip(s_types, o_types, strict=True)])
         if type_conflicts.any():