diff --git a/src/ifcopenshell-python/ifcopenshell/api/type/assign_type.py b/src/ifcopenshell-python/ifcopenshell/api/type/assign_type.py
index 9dd01ee97e..3087811234 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/type/assign_type.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/type/assign_type.py
@@ -193,15 +193,27 @@ class Usecase:
         # The EXPRESS schema has no WHERE rule pairing RelatingType /
         # RelatedObjects classes; the canonical class pairing per schema
         # is a buildingSMART implementer agreement, enforced here.
-        allowed_occurrences = ifcopenshell.util.type.get_applicable_entities(
-            relating_type.is_a(), schema=self.file.schema
+        allowed_occurrences = set(
+            ifcopenshell.util.type.get_applicable_entities(relating_type.is_a(), schema=self.file.schema)
         )
+        # The implementer agreement map has no entry for the abstract
+        # IfcTypeProduct, which Bonsai uses for annotation types. The schema
+        # itself defines IfcTypeProduct.ApplicableOccurrence for exactly this
+        # purpose, so honor it when the leading class token is a valid entity.
+        if applicable_occurrence := getattr(relating_type, "ApplicableOccurrence", None):
+            occurrence_class = applicable_occurrence.split("/", 1)[0]
+            schema = ifcopenshell.schema_by_name(self.file.schema)
+            try:
+                schema.declaration_by_name(occurrence_class)
+                allowed_occurrences.add(occurrence_class)
+            except RuntimeError:
+                pass
         mismatched_classes = sorted({o.is_a() for o in related_objects if o.is_a() not in allowed_occurrences})
         if mismatched_classes:
             raise TypeError(
                 f"{relating_type.is_a()} cannot type {', '.join(mismatched_classes)} "
                 f"in schema {self.file.schema} (allowed occurrence classes: "
-                f"{allowed_occurrences or '<none>'})"
+                f"{', '.join(sorted(allowed_occurrences)) or '<none>'})"
             )
 
         ifc2x3 = self.file.schema == "IFC2X3"