diff --git a/src/openai/_models.py b/src/openai/_models.py
index af71a91850..92dc0447c7 100644
--- a/src/openai/_models.py
+++ b/src/openai/_models.py
@@ -66,7 +66,7 @@
 from ._constants import RAW_RESPONSE_HEADER
 
 if TYPE_CHECKING:
-    from pydantic_core.core_schema import ModelField, ModelSchema, LiteralSchema, ModelFieldsSchema
+    from pydantic_core.core_schema import ModelField, LiteralSchema
 
 __all__ = ["BaseModel", "GenericModel"]
 
@@ -700,18 +700,19 @@ def _build_discriminated_union_meta(*, union: type, meta_annotations: tuple[Any,
 
 def _extract_field_schema_pv2(model: type[BaseModel], field_name: str) -> ModelField | None:
     schema = model.__pydantic_core_schema__
-    if schema["type"] == "definitions":
+    schema_type = schema["type"]
+    if schema_type == "definitions":
         schema = schema["schema"]
+        schema_type = schema["type"]
 
-    if schema["type"] != "model":
+    if schema_type != "model":
         return None
 
-    schema = cast("ModelSchema", schema)
     fields_schema = schema["schema"]
-    if fields_schema["type"] != "model-fields":
+    fields_schema_type = fields_schema["type"]
+    if fields_schema_type != "model-fields":
         return None
 
-    fields_schema = cast("ModelFieldsSchema", fields_schema)
     field = fields_schema["fields"].get(field_name)
     if not field:
         return None