diff --git a/CHANGES.md b/CHANGES.md
index d87de84b..4834220d 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- fixed typing of base_model and mixins parameters ([#852](https://github.com/stac-utils/stac-fastapi/pull/852))
+
 ## [6.0.0] - 2025-06-19
 
 ### Changed
diff --git a/stac_fastapi/api/stac_fastapi/api/models.py b/stac_fastapi/api/stac_fastapi/api/models.py
index 79da7b16..8c0a9fc1 100644
--- a/stac_fastapi/api/stac_fastapi/api/models.py
+++ b/stac_fastapi/api/stac_fastapi/api/models.py
@@ -29,9 +29,9 @@
 
 def create_request_model(
     model_name="SearchGetRequest",
-    base_model: Union[Type[BaseModel], APIRequest] = BaseSearchGetRequest,
+    base_model: Union[Type[BaseModel], Type[APIRequest]] = BaseSearchGetRequest,
     extensions: Optional[List[ApiExtension]] = None,
-    mixins: Optional[Union[List[BaseModel], List[APIRequest]]] = None,
+    mixins: Optional[Union[List[Type[BaseModel]], List[Type[APIRequest]]]] = None,
     request_type: Optional[str] = "GET",
 ) -> Union[Type[BaseModel], APIRequest]:
     """Create a pydantic model for validating request bodies."""