diff --git a/end_to_end_tests/golden-record-custom/custom_e2e/api/tests/defaults_tests_defaults_post.py b/end_to_end_tests/golden-record-custom/custom_e2e/api/tests/defaults_tests_defaults_post.py
index 466b1498d..53e2d1def 100644
--- a/end_to_end_tests/golden-record-custom/custom_e2e/api/tests/defaults_tests_defaults_post.py
+++ b/end_to_end_tests/golden-record-custom/custom_e2e/api/tests/defaults_tests_defaults_post.py
@@ -13,6 +13,7 @@
 
 from ...models.an_enum import AnEnum
 from ...models.http_validation_error import HTTPValidationError
+from ...models.model_with_union_property import ModelWithUnionProperty
 from ...types import UNSET, Unset
 
 
@@ -50,6 +51,8 @@ def httpx_request(
     union_prop: Union[Unset, float, str] = "not a float",
     union_prop_with_ref: Union[Unset, float, AnEnum] = 0.6,
     enum_prop: Union[Unset, AnEnum] = UNSET,
+    model_prop: Union[ModelWithUnionProperty, Unset] = UNSET,
+    required_model_prop: ModelWithUnionProperty,
 ) -> Response[Union[None, HTTPValidationError]]:
 
     json_datetime_prop: Union[Unset, str] = UNSET
@@ -89,6 +92,12 @@ def httpx_request(
     if not isinstance(enum_prop, Unset):
         json_enum_prop = enum_prop
 
+    json_model_prop: Union[Unset, Dict[str, Any]] = UNSET
+    if not isinstance(model_prop, Unset):
+        json_model_prop = model_prop.to_dict()
+
+    json_required_model_prop = required_model_prop.to_dict()
+
     params: Dict[str, Any] = {
         "string_prop": string_prop,
         "datetime_prop": json_datetime_prop,
@@ -101,6 +110,9 @@ def httpx_request(
         "union_prop_with_ref": json_union_prop_with_ref,
         "enum_prop": json_enum_prop,
     }
+    if not isinstance(json_model_prop, Unset):
+        params.update(json_model_prop)
+    params.update(json_required_model_prop)
     params = {k: v for k, v in params.items() if v is not UNSET and v is not None}
 
     response = client.request(
diff --git a/end_to_end_tests/golden-record/my_test_api_client/api/tests/defaults_tests_defaults_post.py b/end_to_end_tests/golden-record/my_test_api_client/api/tests/defaults_tests_defaults_post.py
index b3e6d6dfb..5f5f5dac6 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/api/tests/defaults_tests_defaults_post.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/api/tests/defaults_tests_defaults_post.py
@@ -7,6 +7,7 @@
 from ...client import Client
 from ...models.an_enum import AnEnum
 from ...models.http_validation_error import HTTPValidationError
+from ...models.model_with_union_property import ModelWithUnionProperty
 from ...types import UNSET, Response, Unset
 
 
@@ -23,6 +24,8 @@ def _get_kwargs(
     union_prop: Union[Unset, float, str] = "not a float",
     union_prop_with_ref: Union[Unset, float, AnEnum] = 0.6,
     enum_prop: Union[Unset, AnEnum] = UNSET,
+    model_prop: Union[ModelWithUnionProperty, Unset] = UNSET,
+    required_model_prop: ModelWithUnionProperty,
 ) -> Dict[str, Any]:
     url = "{}/tests/defaults".format(client.base_url)
 
@@ -65,6 +68,12 @@ def _get_kwargs(
     if not isinstance(enum_prop, Unset):
         json_enum_prop = enum_prop
 
+    json_model_prop: Union[Unset, Dict[str, Any]] = UNSET
+    if not isinstance(model_prop, Unset):
+        json_model_prop = model_prop.to_dict()
+
+    json_required_model_prop = required_model_prop.to_dict()
+
     params: Dict[str, Any] = {
         "string_prop": string_prop,
         "datetime_prop": json_datetime_prop,
@@ -77,6 +86,9 @@ def _get_kwargs(
         "union_prop_with_ref": json_union_prop_with_ref,
         "enum_prop": json_enum_prop,
     }
+    if not isinstance(json_model_prop, Unset):
+        params.update(json_model_prop)
+    params.update(json_required_model_prop)
     params = {k: v for k, v in params.items() if v is not UNSET and v is not None}
 
     return {
@@ -122,6 +134,8 @@ def sync_detailed(
     union_prop: Union[Unset, float, str] = "not a float",
     union_prop_with_ref: Union[Unset, float, AnEnum] = 0.6,
     enum_prop: Union[Unset, AnEnum] = UNSET,
+    model_prop: Union[ModelWithUnionProperty, Unset] = UNSET,
+    required_model_prop: ModelWithUnionProperty,
 ) -> Response[Union[None, HTTPValidationError]]:
     kwargs = _get_kwargs(
         client=client,
@@ -135,6 +149,8 @@ def sync_detailed(
         union_prop=union_prop,
         union_prop_with_ref=union_prop_with_ref,
         enum_prop=enum_prop,
+        model_prop=model_prop,
+        required_model_prop=required_model_prop,
     )
 
     response = httpx.post(
@@ -157,6 +173,8 @@ def sync(
     union_prop: Union[Unset, float, str] = "not a float",
     union_prop_with_ref: Union[Unset, float, AnEnum] = 0.6,
     enum_prop: Union[Unset, AnEnum] = UNSET,
+    model_prop: Union[ModelWithUnionProperty, Unset] = UNSET,
+    required_model_prop: ModelWithUnionProperty,
 ) -> Optional[Union[None, HTTPValidationError]]:
     """  """
 
@@ -172,6 +190,8 @@ def sync(
         union_prop=union_prop,
         union_prop_with_ref=union_prop_with_ref,
         enum_prop=enum_prop,
+        model_prop=model_prop,
+        required_model_prop=required_model_prop,
     ).parsed
 
 
@@ -188,6 +208,8 @@ async def asyncio_detailed(
     union_prop: Union[Unset, float, str] = "not a float",
     union_prop_with_ref: Union[Unset, float, AnEnum] = 0.6,
     enum_prop: Union[Unset, AnEnum] = UNSET,
+    model_prop: Union[ModelWithUnionProperty, Unset] = UNSET,
+    required_model_prop: ModelWithUnionProperty,
 ) -> Response[Union[None, HTTPValidationError]]:
     kwargs = _get_kwargs(
         client=client,
@@ -201,6 +223,8 @@ async def asyncio_detailed(
         union_prop=union_prop,
         union_prop_with_ref=union_prop_with_ref,
         enum_prop=enum_prop,
+        model_prop=model_prop,
+        required_model_prop=required_model_prop,
     )
 
     async with httpx.AsyncClient() as _client:
@@ -222,6 +246,8 @@ async def asyncio(
     union_prop: Union[Unset, float, str] = "not a float",
     union_prop_with_ref: Union[Unset, float, AnEnum] = 0.6,
     enum_prop: Union[Unset, AnEnum] = UNSET,
+    model_prop: Union[ModelWithUnionProperty, Unset] = UNSET,
+    required_model_prop: ModelWithUnionProperty,
 ) -> Optional[Union[None, HTTPValidationError]]:
     """  """
 
@@ -238,5 +264,7 @@ async def asyncio(
             union_prop=union_prop,
             union_prop_with_ref=union_prop_with_ref,
             enum_prop=enum_prop,
+            model_prop=model_prop,
+            required_model_prop=required_model_prop,
         )
     ).parsed
diff --git a/end_to_end_tests/openapi.json b/end_to_end_tests/openapi.json
index 196538f19..881fe2be5 100644
--- a/end_to_end_tests/openapi.json
+++ b/end_to_end_tests/openapi.json
@@ -396,6 +396,22 @@
             },
             "name": "enum_prop",
             "in": "query"
+          },
+          {
+            "required": false,
+            "schema": {
+              "$ref": "#/components/schemas/ModelWithUnionProperty"
+            },
+            "name": "model_prop",
+            "in": "query"
+          },
+          {
+            "required": true,
+            "schema": {
+              "$ref": "#/components/schemas/ModelWithUnionProperty"
+            },
+            "name": "required_model_prop",
+            "in": "query"
           }
         ],
         "responses": {
diff --git a/openapi_python_client/parser/properties/model_property.py b/openapi_python_client/parser/properties/model_property.py
index d5b15e866..1cf3e455c 100644
--- a/openapi_python_client/parser/properties/model_property.py
+++ b/openapi_python_client/parser/properties/model_property.py
@@ -19,6 +19,7 @@ class ModelProperty(Property):
     additional_properties: Union[bool, Property]
 
     template: ClassVar[str] = "model_property.py.jinja"
+    json_is_dict: ClassVar[bool] = True
 
     def get_type_string(self, no_optional: bool = False) -> str:
         """ Get a string representation of type that should be used when declaring this property """
diff --git a/openapi_python_client/parser/properties/property.py b/openapi_python_client/parser/properties/property.py
index 0b7047551..a94af72ba 100644
--- a/openapi_python_client/parser/properties/property.py
+++ b/openapi_python_client/parser/properties/property.py
@@ -28,6 +28,7 @@ class Property:
     python_name: str = attr.ib(init=False)
 
     template: ClassVar[Optional[str]] = None
+    json_is_dict: ClassVar[bool] = False
 
     def __attrs_post_init__(self) -> None:
         object.__setattr__(self, "python_name", utils.to_valid_python_identifier(utils.snake_case(self.name)))
diff --git a/openapi_python_client/templates/endpoint_macros.py.jinja b/openapi_python_client/templates/endpoint_macros.py.jinja
index 2b86668e3..113c410e2 100644
--- a/openapi_python_client/templates/endpoint_macros.py.jinja
+++ b/openapi_python_client/templates/endpoint_macros.py.jinja
@@ -22,13 +22,26 @@ if {{ parameter.python_name }} is not UNSET:
     {% endfor %}
 params: Dict[str, Any] = {
     {% for property in endpoint.query_parameters %}
-        {% if property.template %}
+        {% if not property.json_is_dict %}
+            {% if property.template %}
     "{{ property.name }}": {{ "json_" + property.python_name }},
-        {% else %}
+            {% else %}
     "{{ property.name }}": {{ property.python_name }},
+            {% endif %}
         {% endif %}
     {% endfor %}
 }
+    {% for property in endpoint.query_parameters %}
+        {% if property.json_is_dict %}
+            {% set property_name = "json_" + property.python_name %}
+            {% if property.required and not property.nullable %}
+params.update({{ property_name }})
+            {% else %}
+if {% if not property.required %}not isinstance({{ property_name }}, Unset){% endif %}{% if not property.required and property.nullable %} and {% endif %}{% if property.nullable %}{{ property_name }} is not None{% endif %}:
+    params.update({{ property_name }})
+            {% endif %}
+        {% endif %}
+    {% endfor %}
 params = {k: v for k, v in params.items() if v is not UNSET and v is not None}
 {% endif %}
 {% endmacro %}