diff --git a/fastapi/encoders.py b/fastapi/encoders.py
index 451ea0760..c416abbcb 100644
--- a/fastapi/encoders.py
+++ b/fastapi/encoders.py
@@ -240,7 +240,7 @@ def jsonable_encoder(
             custom_encoder=encoders,
             sqlalchemy_safe=sqlalchemy_safe,
         )
-    if dataclasses.is_dataclass(obj):
+    if dataclasses.is_dataclass(type(obj)):
         obj_dict = dataclasses.asdict(obj)
         return jsonable_encoder(
             obj_dict,
diff --git a/fastapi/routing.py b/fastapi/routing.py
index 54c75a027..40c66f2f2 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -119,7 +119,7 @@ def _prepare_response_content(
             )
             for k, v in res.items()
         }
-    elif dataclasses.is_dataclass(res):
+    elif dataclasses.is_dataclass(type(res)):
         return dataclasses.asdict(res)
     return res
 
diff --git a/fastapi/security/api_key.py b/fastapi/security/api_key.py
index 70c2dca8a..6d6dd01d9 100644
--- a/fastapi/security/api_key.py
+++ b/fastapi/security/api_key.py
@@ -100,7 +100,7 @@ class APIKeyQuery(APIKeyBase):
         ] = True,
     ):
         self.model: APIKey = APIKey(
-            **{"in": APIKeyIn.query},  # type: ignore[arg-type]
+            **{"in": APIKeyIn.query},
             name=name,
             description=description,
         )
@@ -188,7 +188,7 @@ class APIKeyHeader(APIKeyBase):
         ] = True,
     ):
         self.model: APIKey = APIKey(
-            **{"in": APIKeyIn.header},  # type: ignore[arg-type]
+            **{"in": APIKeyIn.header},
             name=name,
             description=description,
         )
@@ -276,7 +276,7 @@ class APIKeyCookie(APIKeyBase):
         ] = True,
     ):
         self.model: APIKey = APIKey(
-            **{"in": APIKeyIn.cookie},  # type: ignore[arg-type]
+            **{"in": APIKeyIn.cookie},
             name=name,
             description=description,
         )
diff --git a/pyproject.toml b/pyproject.toml
index 7709451ff..bf0e10a8e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -142,6 +142,7 @@ source-includes = [
 name = "fastapi-slim"
 
 [tool.mypy]
+plugins = ["pydantic.mypy"]
 strict = true
 
 [[tool.mypy.overrides]]
diff --git a/requirements-tests.txt b/requirements-tests.txt
index b9f2b2b66..cbe5599b9 100644
--- a/requirements-tests.txt
+++ b/requirements-tests.txt
@@ -2,7 +2,7 @@
 -r requirements-docs-tests.txt
 pytest >=7.1.3,<9.0.0
 coverage[toml] >= 6.5.0,< 8.0
-mypy ==1.8.0
+mypy ==1.14.1
 dirty-equals ==0.9.0
 sqlmodel==0.0.24
 flask >=1.1.2,<4.0.0