diff --git a/masque/pattern.py b/masque/pattern.py
index 287ca92..b670493 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -1383,6 +1383,15 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
         if not skip_port_check:
             self.check_ports(other.ports.keys(), map_in=None, map_out=port_map)
 
+        if not skip_geometry:
+            if append:
+                if isinstance(other, Abstract):
+                    raise PatternError('Must provide a full `Pattern` (not an `Abstract`) when appending!')
+            else:
+                if isinstance(other, Pattern):
+                    raise PatternError('Must provide an `Abstract` (not a `Pattern`) when creating a reference. '
+                                       'Use `append=True` if you intended to append the full geometry.')
+
         ports = {}
         for name, port in other.ports.items():
             new_name = port_map.get(name, name)
@@ -1404,8 +1413,6 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             return self
 
         if append:
-            if isinstance(other, Abstract):
-                raise PatternError('Must provide a full `Pattern` (not an `Abstract`) when appending!')
             other_copy = other.deepcopy()
             other_copy.ports.clear()
             if mirrored:
@@ -1414,9 +1421,6 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             other_copy.translate_elements(offset)
             self.append(other_copy)
         else:
-            if isinstance(other, Pattern):
-                raise PatternError('Must provide an `Abstract` (not a `Pattern`) when creating a reference. '
-                                   'Use `append=True` if you intended to append the full geometry.')
             ref = Ref(mirrored=mirrored)
             ref.rotate_around(pivot, rotation)
             ref.translate(offset)
@@ -1554,6 +1558,13 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             map_out = {out_port_name: next(iter(map_in.keys()))}
 
         self.check_ports(other.ports.keys(), map_in, map_out)
+        if not skip_geometry:
+            if append:
+                if isinstance(other, Abstract):
+                    raise PatternError('Must provide a full `Pattern` (not an `Abstract`) when appending!')
+            elif isinstance(other, Pattern):
+                raise PatternError('Must provide an `Abstract` (not a `Pattern`) when creating a reference. '
+                                   'Use `append=True` if you intended to append the full geometry.')
         try:
             translation, rotation, pivot = self.find_transform(
                 other,
@@ -1587,10 +1598,6 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             self._log_port_removal(ki)
             map_out[vi] = None
 
-        if isinstance(other, Pattern) and not (append or skip_geometry):
-            raise PatternError('Must provide an `Abstract` (not a `Pattern`) when creating a reference. '
-                               'Use `append=True` if you intended to append the full geometry.')
-
         self.place(
             other,
             offset = translation,
@@ -1662,9 +1669,13 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
         else:
             raise PatternError(f'Unable to get ports from {type(source)}: {source}')
 
-        if port_map:
+        if port_map is not None:
             if isinstance(port_map, dict):
                 missing_inkeys = set(port_map.keys()) - set(orig_ports.keys())
+                port_targets = list(port_map.values())
+                duplicate_targets = {vv for vv in port_targets if port_targets.count(vv) > 1}
+                if duplicate_targets:
+                    raise PortError(f'Duplicate targets in `port_map`: {duplicate_targets}')
                 mapped_ports = {port_map[k]: v for k, v in orig_ports.items() if k in port_map}
             else:
                 port_set = set(port_map)
diff --git a/masque/test/test_pattern.py b/masque/test/test_pattern.py
index 59cc225..6048bf1 100644
--- a/masque/test/test_pattern.py
+++ b/masque/test/test_pattern.py
@@ -5,10 +5,11 @@ from numpy.testing import assert_equal, assert_allclose
 from numpy import pi
 
 from ..error import PatternError
+from ..abstract import Abstract
 from ..pattern import Pattern
 from ..shapes import Polygon
 from ..ref import Ref
-from ..ports import Port
+from ..ports import Port, PortError
 from ..label import Label
 from ..repetition import Grid
 
@@ -134,6 +135,18 @@ def test_pattern_place_requires_abstract_for_reference() -> None:
     with pytest.raises(PatternError, match='Must provide an `Abstract`'):
         parent.place(child)
 
+    assert not parent.ports
+
+
+def test_pattern_place_append_requires_pattern_atomically() -> None:
+    parent = Pattern()
+    child = Abstract("child", {"A": Port((1, 2), 0)})
+
+    with pytest.raises(PatternError, match='Must provide a full `Pattern`'):
+        parent.place(child, append=True)
+
+    assert not parent.ports
+
 
 def test_pattern_interface() -> None:
     source = Pattern()
@@ -151,6 +164,34 @@ def test_pattern_interface() -> None:
     assert iface.ports["out_A"].ptype == "test"
 
 
+def test_pattern_interface_duplicate_port_map_targets_raise() -> None:
+    source = Pattern()
+    source.ports["A"] = Port((10, 20), 0)
+    source.ports["B"] = Port((30, 40), pi)
+
+    with pytest.raises(PortError, match='Duplicate targets in `port_map`'):
+        Pattern.interface(source, port_map={"A": "X", "B": "X"})
+
+
+def test_pattern_interface_empty_port_map_copies_no_ports() -> None:
+    source = Pattern()
+    source.ports["A"] = Port((10, 20), 0)
+    source.ports["B"] = Port((30, 40), pi)
+
+    assert not Pattern.interface(source, port_map={}).ports
+    assert not Pattern.interface(source, port_map=[]).ports
+
+
+def test_pattern_plug_requires_abstract_for_reference_atomically() -> None:
+    parent = Pattern(ports={"X": Port((0, 0), 0)})
+    child = Pattern(ports={"A": Port((0, 0), pi)})
+
+    with pytest.raises(PatternError, match='Must provide an `Abstract`'):
+        parent.plug(child, {"X": "A"})
+
+    assert set(parent.ports) == {"X"}
+
+
 def test_pattern_append_port_conflict_is_atomic() -> None:
     pat1 = Pattern()
     pat1.ports["A"] = Port((0, 0), 0)