diff --git a/fastapi/openapi/models.py b/fastapi/openapi/models.py
index ed07b40f5..d79887413 100644
--- a/fastapi/openapi/models.py
+++ b/fastapi/openapi/models.py
@@ -157,7 +157,7 @@ class Schema(BaseModelWithConfig):
     unevaluatedProperties: Optional["SchemaOrBool"] = None
     # Ref: JSON Schema Validation 2020-12: https://json-schema.org/draft/2020-12/json-schema-validation.html#name-a-vocabulary-for-structural
     # A Vocabulary for Structural Validation
-    type: Optional[str] = None
+    type: Optional[Union[str, Set[str]]] = None
     enum: Optional[List[Any]] = None
     const: Optional[Any] = None
     multipleOf: Optional[float] = Field(default=None, gt=0)
diff --git a/tests/test_custom_schema_fields.py b/tests/test_custom_schema_fields.py
index ee51fc7ff..cd1d3f9f9 100644
--- a/tests/test_custom_schema_fields.py
+++ b/tests/test_custom_schema_fields.py
@@ -1,7 +1,14 @@
+from typing import Optional
+
+from dirty_equals import IsList
 from fastapi import FastAPI
 from fastapi._compat import PYDANTIC_V2
 from fastapi.testclient import TestClient
 from pydantic import BaseModel
+from typing_extensions import Annotated
+
+if PYDANTIC_V2:
+    from pydantic.json_schema import WithJsonSchema
 
 app = FastAPI()
 
@@ -10,12 +17,17 @@ class Item(BaseModel):
     name: str
 
     if PYDANTIC_V2:
+        description: Annotated[
+            Optional[str], WithJsonSchema({"type": ["string", "null"]})
+        ] = None
+
         model_config = {
             "json_schema_extra": {
                 "x-something-internal": {"level": 4},
             }
         }
     else:
+        description: Optional[str] = None  # type: ignore[no-redef]
 
         class Config:
             schema_extra = {
@@ -42,7 +54,18 @@ item_schema = {
         "name": {
             "title": "Name",
             "type": "string",
-        }
+        },
+        "description": (
+            {
+                "title": "Description",
+                "type": IsList("string", "null", check_order=False),
+            }
+            if PYDANTIC_V2
+            else {
+                "title": "Description",
+                "type": "string",
+            }
+        ),
     },
 }
 
@@ -57,4 +80,4 @@ def test_response():
     # For coverage
     response = client.get("/foo")
     assert response.status_code == 200, response.text
-    assert response.json() == {"name": "Foo item"}
+    assert response.json() == {"name": "Foo item", "description": None}