diff --git a/masque/builder/builder.py b/masque/builder/builder.py
index b92c9ac..b8b00be 100644
--- a/masque/builder/builder.py
+++ b/masque/builder/builder.py
@@ -226,6 +226,7 @@ class Builder(PortList):
             inherit_name: bool = True,
             set_rotation: bool | None = None,
             append: bool = False,
+            ok_connections: Iterable[tuple[str, str]] = (),
             ) -> Self:
         """
         Wrapper around `Pattern.plug` which allows a string for `other`.
@@ -260,6 +261,11 @@ class Builder(PortList):
             append: If `True`, `other` is appended instead of being referenced.
                 Note that this does not flatten  `other`, so its refs will still
                 be refs (now inside `self`).
+            ok_connections: Set of "allowed" ptype combinations. Identical
+                ptypes are always allowed to connect, as is `'unk'` with
+                any other ptypte. Non-allowed ptype connections will emit a
+                warning. Order is ignored, i.e. `(a, b)` is equivalent to
+                `(b, a)`.
 
         Returns:
             self
@@ -293,6 +299,7 @@ class Builder(PortList):
             inherit_name=inherit_name,
             set_rotation=set_rotation,
             append=append,
+            ok_connections=ok_connections,
             )
         return self
 
diff --git a/masque/pattern.py b/masque/pattern.py
index 1816762..0ae230d 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -1225,6 +1225,7 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             inherit_name: bool = True,
             set_rotation: bool | None = None,
             append: bool = False,
+            ok_connections: Iterable[tuple[str, str]] = (),
             ) -> Self:
         """
         Instantiate or append a pattern into the current pattern, connecting
@@ -1270,6 +1271,11 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             append: If `True`, `other` is appended instead of being referenced.
                 Note that this does not flatten  `other`, so its refs will still
                 be refs (now inside `self`).
+            ok_connections: Set of "allowed" ptype combinations. Identical
+                ptypes are always allowed to connect, as is `'unk'` with
+                any other ptypte. Non-allowed ptype connections will emit a
+                warning. Order is ignored, i.e. `(a, b)` is equivalent to
+                `(b, a)`.
 
         Returns:
             self
@@ -1300,6 +1306,7 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             map_in,
             mirrored=mirrored,
             set_rotation=set_rotation,
+            ok_connections=ok_connections,
             )
 
         # get rid of plugged ports
diff --git a/masque/ports.py b/masque/ports.py
index 90ba729..e85b2d9 100644
--- a/masque/ports.py
+++ b/masque/ports.py
@@ -419,6 +419,7 @@ class PortList(metaclass=ABCMeta):
             *,
             mirrored: bool = False,
             set_rotation: bool | None = None,
+            ok_connections: Iterable[tuple[str, str]] = (),
             ) -> tuple[NDArray[numpy.float64], float, NDArray[numpy.float64]]:
         """
         Given a device `other` and a mapping `map_in` specifying port connections,
@@ -435,6 +436,11 @@ class PortList(metaclass=ABCMeta):
                 port with `rotation=None`), `set_rotation` must be provided
                 to indicate how much `other` should be rotated. Otherwise,
                 `set_rotation` must remain `None`.
+            ok_connections: Set of "allowed" ptype combinations. Identical
+                ptypes are always allowed to connect, as is `'unk'` with
+                any other ptypte. Non-allowed ptype connections will emit a
+                warning. Order is ignored, i.e. `(a, b)` is equivalent to
+                `(b, a)`.
 
         Returns:
             - The (x, y) translation (performed last)
@@ -451,6 +457,7 @@ class PortList(metaclass=ABCMeta):
             map_in=map_in,
             mirrored=mirrored,
             set_rotation=set_rotation,
+            ok_connections=ok_connections,
             )
 
     @staticmethod
@@ -461,6 +468,7 @@ class PortList(metaclass=ABCMeta):
             *,
             mirrored: bool = False,
             set_rotation: bool | None = None,
+            ok_connections: Iterable[tuple[str, str]] = (),
             ) -> tuple[NDArray[numpy.float64], float, NDArray[numpy.float64]]:
         """
         Given two sets of ports (s_ports and o_ports) and a mapping `map_in`
@@ -479,6 +487,11 @@ class PortList(metaclass=ABCMeta):
                 port with `rotation=None`), `set_rotation` must be provided
                 to indicate how much `o_ports` should be rotated. Otherwise,
                 `set_rotation` must remain `None`.
+            ok_connections: Set of "allowed" ptype combinations. Identical
+                ptypes are always allowed to connect, as is `'unk'` with
+                any other ptypte. Non-allowed ptype connections will emit a
+                warning. Order is ignored, i.e. `(a, b)` is equivalent to
+                `(b, a)`.
 
         Returns:
             - The (x, y) translation (performed last)
@@ -502,7 +515,8 @@ class PortList(metaclass=ABCMeta):
             o_offsets[:, 1] *= -1
             o_rotations *= -1
 
-        type_conflicts = numpy.array([st != ot and 'unk' not in (st, ot)
+        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():
             msg = 'Ports have conflicting types:\n'