diff --git a/changelog.d/11677.bugfix b/changelog.d/11677.bugfix
new file mode 100644
index 0000000000000000000000000000000000000000..5691064a303cd432ce07aed09d7d469e60aa6793
--- /dev/null
+++ b/changelog.d/11677.bugfix
@@ -0,0 +1 @@
+Fix wrong variable reference in `SimpleHttpClient.get_json` that results in the absence of the `Accept` header in the request.
diff --git a/synapse/http/client.py b/synapse/http/client.py
index fbbeceabeb6ac040ba2946f455dfc5b532a83008..ca33b45cb21f903cfaa0e180b77036f799e2cffb 100644
--- a/synapse/http/client.py
+++ b/synapse/http/client.py
@@ -588,7 +588,7 @@ class SimpleHttpClient:
         if headers:
             actual_headers.update(headers)  # type: ignore
 
-        body = await self.get_raw(uri, args, headers=headers)
+        body = await self.get_raw(uri, args, headers=actual_headers)
         return json_decoder.decode(body.decode("utf-8"))
 
     async def put_json(