diff --git a/spiderweb/middleware/__init__.py b/spiderweb/middleware/__init__.py
index 9118034..9ebff28 100644
--- a/spiderweb/middleware/__init__.py
+++ b/spiderweb/middleware/__init__.py
@@ -63,7 +63,7 @@ class MiddlewareMixin:
 
     def post_process_middleware(
         self, request: Request, response: HttpResponse, rendered_response: str
-    ) -> str:
+    ) -> str | bytes:
         # run them in reverse order, same as process_response. The top of the middleware
         # stack should be the first and last middleware to run.
         for middleware in reversed(self.middleware):
diff --git a/spiderweb/middleware/gzip.py b/spiderweb/middleware/gzip.py
index 00982b1..6610a6d 100644
--- a/spiderweb/middleware/gzip.py
+++ b/spiderweb/middleware/gzip.py
@@ -41,7 +41,7 @@ class GzipMiddleware(SpiderwebMiddleware):
 
     def post_process(
         self, request: Request, response: HttpResponse, rendered_response: str
-    ) -> str:
+    ) -> str | bytes:
         # Only actually compress the response if the following attributes are true:
         #
         # * The response status code is a 2xx success code