diff --git a/sdks/python/apache_beam/transforms/external.py b/sdks/python/apache_beam/transforms/external.py
index 4b8e708bfc5c..44bf2398a6dd 100644
--- a/sdks/python/apache_beam/transforms/external.py
+++ b/sdks/python/apache_beam/transforms/external.py
@@ -185,6 +185,14 @@ def __init__(self, identifier, **kwargs):
     self._identifier = identifier
     self._kwargs = kwargs
 
+  def identifier(self):
+    """
+    The URN referencing this SchemaTransform
+
+    :return: str
+    """
+    return self._identifier
+
   def build(self):
     schema_proto, payload = self._get_schema_proto_and_payload(**self._kwargs)
     payload = external_transforms_pb2.SchemaTransformPayload(
@@ -194,7 +202,7 @@ def build(self):
     return payload
 
 
-class ExplicitSchemaTransformPayloadBuilder(PayloadBuilder):
+class ExplicitSchemaTransformPayloadBuilder(SchemaTransformPayloadBuilder):
   def __init__(self, identifier, schema_proto, **kwargs):
     self._identifier = identifier
     self._schema_proto = schema_proto
@@ -414,7 +422,7 @@ def __init__(
 
   def expand(self, pcolls):
     # Expand the transform using the expansion service.
-    return pcolls | ExternalTransform(
+    return pcolls | self._payload_builder.identifier() >> ExternalTransform(
         common_urns.schematransform_based_expand.urn,
         self._payload_builder,
         self._expansion_service)