diff --git a/setup/base/base.go b/setup/base/base.go
index 70021bb8a..dbb236956 100644
--- a/setup/base/base.go
+++ b/setup/base/base.go
@@ -381,21 +381,6 @@ func (b *BaseDendrite) SetupAndServeHTTP(
 	externalRouter := mux.NewRouter().SkipClean(true).UseEncodedPath()
 	internalRouter := externalRouter
 
-	notFoundHandler := func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusNotFound)
-		_, _ = w.Write([]byte("endpoint not found"))
-	}
-	notAllowedHandler := func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusMethodNotAllowed)
-		_, _ = w.Write([]byte(fmt.Sprintf("%s not allowed on this endpoint", r.Method)))
-	}
-
-	notFoundCORSHandler := httputil.WrapHandlerInCORS(http.HandlerFunc(notFoundHandler))
-	notAllowedCORSHandler := httputil.WrapHandlerInCORS(http.HandlerFunc(notAllowedHandler))
-
-	externalRouter.NotFoundHandler = notFoundCORSHandler
-	externalRouter.MethodNotAllowedHandler = notAllowedCORSHandler
-
 	externalServ := &http.Server{
 		Addr:         string(externalAddr),
 		WriteTimeout: HTTPServerTimeout,
@@ -415,8 +400,6 @@ func (b *BaseDendrite) SetupAndServeHTTP(
 		// without enabling TLS.
 		internalH2S := &http2.Server{}
 		internalRouter = mux.NewRouter().SkipClean(true).UseEncodedPath()
-		internalRouter.NotFoundHandler = notFoundCORSHandler
-		internalRouter.MethodNotAllowedHandler = notAllowedCORSHandler
 		internalServ = &http.Server{
 			Addr:    string(internalAddr),
 			Handler: h2c.NewHandler(internalRouter, internalH2S),
@@ -426,6 +409,29 @@ func (b *BaseDendrite) SetupAndServeHTTP(
 		}
 	}
 
+	notFoundHandler := func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+		_, _ = w.Write([]byte("endpoint not found"))
+	}
+	notAllowedHandler := func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusMethodNotAllowed)
+		_, _ = w.Write([]byte(fmt.Sprintf("%s not allowed on this endpoint", r.Method)))
+	}
+
+	notFoundCORSHandler := httputil.WrapHandlerInCORS(http.HandlerFunc(notFoundHandler))
+	notAllowedCORSHandler := httputil.WrapHandlerInCORS(http.HandlerFunc(notAllowedHandler))
+
+	for _, router := range []*mux.Router{
+		internalRouter, externalRouter,
+		b.DendriteAdminMux, b.SynapseAdminMux,
+		b.InternalAPIMux, b.PublicWellKnownAPIMux,
+		b.PublicClientAPIMux, b.PublicFederationAPIMux,
+		b.PublicKeyAPIMux, b.PublicMediaAPIMux,
+	} {
+		router.NotFoundHandler = notFoundCORSHandler
+		router.MethodNotAllowedHandler = notAllowedCORSHandler
+	}
+
 	internalRouter.PathPrefix(httputil.InternalPathPrefix).Handler(b.InternalAPIMux)
 	if b.Cfg.Global.Metrics.Enabled {
 		internalRouter.Handle("/metrics", httputil.WrapHandlerInBasicAuth(promhttp.Handler(), b.Cfg.Global.Metrics.BasicAuth))