diff --git a/nixos/modules/services/matrix/synapse.md b/nixos/modules/services/matrix/synapse.md
index 1d22805b472f..58be24204fcf 100644
--- a/nixos/modules/services/matrix/synapse.md
+++ b/nixos/modules/services/matrix/synapse.md
@@ -31,7 +31,7 @@ let
   clientConfig."m.homeserver".base_url = baseUrl;
   serverConfig."m.server" = "${fqdn}:443";
   mkWellKnown = data: ''
-    add_header Content-Type application/json;
+    default_type application/json;
     add_header Access-Control-Allow-Origin *;
     return 200 '${builtins.toJSON data}';
   '';