diff --git a/drf_spectacular/openapi.py b/drf_spectacular/openapi.py
index 96730675..2c7fc873 100644
--- a/drf_spectacular/openapi.py
+++ b/drf_spectacular/openapi.py
@@ -751,7 +751,7 @@ def _get_response_bodies(self, path, method):
         elif isinstance(response_serializers, dict):
             # custom handling for overriding default return codes with @extend_schema
             return {
-                code: self._get_response_for_code(path, method, serializer)
+                str(code): self._get_response_for_code(path, method, serializer)
                 for code, serializer in response_serializers.items()
             }
         else:
diff --git a/tests/test_extend_schema.yml b/tests/test_extend_schema.yml
index f36739a4..b8d8ebd5 100644
--- a/tests/test_extend_schema.yml
+++ b/tests/test_extend_schema.yml
@@ -42,7 +42,7 @@ paths:
       - {}
       deprecated: true
       responses:
-        201:
+        '201':
           content:
             application/json:
               schema:
@@ -50,13 +50,13 @@ paths:
                 items:
                   $ref: '#/components/schemas/Beta'
           description: ''
-        200:
+        '200':
           content:
             application/json:
               schema:
                 $ref: '#/components/schemas/Gamma'
           description: ''
-        500:
+        '500':
           content:
             application/json:
               schema:
@@ -94,7 +94,7 @@ paths:
       - basicAuth: []
       - {}
       responses:
-        201:
+        '201':
           description: No response body
   /doesitall/manual/:
     post:
@@ -166,7 +166,7 @@ paths:
       - basicAuth: []
       - {}
       responses:
-        204:
+        '204':
           description: No response body
   /doesitall/serializer-query/:
     get:
@@ -222,7 +222,7 @@ paths:
       - basicAuth: []
       - {}
       responses:
-        201:
+        '201':
           description: No response body
 components:
   securitySchemes: