diff --git a/falcon/app_helpers.py b/falcon/app_helpers.py
index 0f9893288..5f34bbed5 100644
--- a/falcon/app_helpers.py
+++ b/falcon/app_helpers.py
@@ -316,7 +316,7 @@ def default_serialize_error(req: Request, resp: Response, exception: HTTPError)
             preferred = req.client_prefers(list(resp.options.media_handlers))
 
     if preferred is not None:
-        handler, serialize_sync, _ = resp.options.media_handlers._resolve(
+        handler, _, _ = resp.options.media_handlers._resolve(
             preferred, MEDIA_JSON, raise_not_found=False
         )
         if preferred == MEDIA_JSON:
@@ -325,12 +325,10 @@ def default_serialize_error(req: Request, resp: Response, exception: HTTPError)
             # media_handlers.
             resp.data = exception.to_json(handler)
         elif handler:
-            if serialize_sync:
-                resp.data = serialize_sync(exception.to_dict(), preferred)
-            else:
-                # NOTE(caselit): Let the app serialize the response if there is no sync
-                # serializer implemented in the handler.
-                resp.media = exception.to_dict()
+            # NOTE(caselit): Let the app serialize the response even if it needs
+            # to re-get the handler, since async handlers may not have a sync
+            # version available.
+            resp.media = exception.to_dict()
         else:
             resp.data = exception.to_xml()
 
diff --git a/falcon/asgi/app.py b/falcon/asgi/app.py
index d28c8c49a..dca7afd96 100644
--- a/falcon/asgi/app.py
+++ b/falcon/asgi/app.py
@@ -566,7 +566,9 @@ async def __call__(  # type: ignore[override] # noqa: C901
                             )
 
                             if serialize_sync:
-                                resp._media_rendered = serialize_sync(resp._media)
+                                resp._media_rendered = serialize_sync(
+                                    resp._media, resp.content_type
+                                )
                             else:
                                 resp._media_rendered = await handler.serialize_async(
                                     resp._media, resp.content_type
diff --git a/tests/test_httperror.py b/tests/test_httperror.py
index ba368f186..093df6c54 100644
--- a/tests/test_httperror.py
+++ b/tests/test_httperror.py
@@ -972,19 +972,19 @@ def test_kw_only(self):
 
 
 class FakeYamlMediaHandler(BaseHandler):
-    def serialize(self, media, content_type):
+    def serialize(self, media, content_type=None):
         assert media == {'title': '410 Gone'}
         return b'title: 410 Gone!'
 
 
 class AsyncOnlyMediaHandler(BaseHandler):
-    async def serialize_async(self, media, content_type):
+    async def serialize_async(self, media, content_type=None):
         assert media == {'title': '410 Gone'}
         return b'this is async'
 
 
 class SyncInterfaceMediaHandler(AsyncOnlyMediaHandler):
-    def serialize(self, media, content_type):
+    def serialize(self, media, content_type=None):
         assert media == {'title': '410 Gone'}
         return b'this is sync instead'