diff --git a/end_to_end_tests/golden-record/my_test_api_client/api/tests/get_user_list.py b/end_to_end_tests/golden-record/my_test_api_client/api/tests/get_user_list.py
index ec2216810..2ed83e388 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/api/tests/get_user_list.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/api/tests/get_user_list.py
@@ -61,6 +61,10 @@ def _parse_response(*, response: httpx.Response) -> Optional[Union[List[AModel],
         response_422 = HTTPValidationError.from_dict(response.json())
 
         return response_422
+    if response.status_code == 423:
+        response_423 = HTTPValidationError.from_dict(response.json())
+
+        return response_423
     return None
 
 
diff --git a/end_to_end_tests/openapi.json b/end_to_end_tests/openapi.json
index 359419473..ed0de8918 100644
--- a/end_to_end_tests/openapi.json
+++ b/end_to_end_tests/openapi.json
@@ -70,6 +70,16 @@
                 }
               }
             }
+          },
+          "423": {
+            "description": "Validation Error",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/HTTPValidationError"
+                }
+              }
+            }
           }
         }
       }
diff --git a/openapi_python_client/templates/endpoint_macros.py.jinja b/openapi_python_client/templates/endpoint_macros.py.jinja
index 705985aab..0f721f714 100644
--- a/openapi_python_client/templates/endpoint_macros.py.jinja
+++ b/openapi_python_client/templates/endpoint_macros.py.jinja
@@ -71,6 +71,12 @@ params = {k: v for k, v in params.items() if v is not UNSET and v is not None}
 {% endif %}
 {% endmacro %}
 
+{% macro reponses_type_csv(responses) %}
+{% for response in responses %}
+{{ response.prop.get_type_string() }}{{"," if not loop.last }}
+{% endfor %}
+{% endmacro %}
+
 {% macro return_type(endpoint) %}
 {% if endpoint.responses | length == 0 %}
 None
@@ -78,8 +84,9 @@ None
 {{ endpoint.responses[0].prop.get_type_string() }}
 {%- else %}
 Union[
-    {% for response in endpoint.responses %}
-    {{ response.prop.get_type_string() }}{{ "," if not loop.last }}
+    {% set response_types = reponses_type_csv(endpoint.responses) | trim  %}
+    {% for type_string in (response_types.split(',') | unique | list) %}
+    {{ type_string }}{{ "," if not loop.last }}
     {% endfor %}
 ]
 {%- endif %}