diff --git a/graphql_server/__init__.py b/graphql_server/__init__.py
index 8db8847..2b58f27 100644
--- a/graphql_server/__init__.py
+++ b/graphql_server/__init__.py
@@ -182,7 +182,7 @@ def execute_graphql_request(schema, params, allow_only_query=False, **kwargs):
                 405,
                 'Can only perform a {} operation from a POST request.'.format(operation_ast.operation),
                 headers={
-                    'Allow': ['POST'],
+                    'Allow': 'POST',
                 }
             )