diff --git a/masque/pattern.py b/masque/pattern.py
index 94068c9..46b564a 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -1576,8 +1576,9 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             self._log_port_removal(ki)
             map_out[vi] = None
 
-        if isinstance(other, Pattern):
-            assert append or skip_geometry, 'Got a name (not an abstract) but was asked to reference (not append)'
+        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,