diff --git a/api.go b/api.go
index 5302a36..5a12180 100644
--- a/api.go
+++ b/api.go
@@ -85,6 +85,10 @@ func (r *Router) handleConfigHTTP(w http.ResponseWriter, req *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		w.Write(configJSON)
 	case http.MethodPut:
+		if r.updatingConfig {
+			http.Error(w, "Config update in progress.", http.StatusConflict)
+			return
+		}
 		var newConfig config.Config
 		err := json.NewDecoder(req.Body).Decode(&newConfig)
 		if err != nil {
diff --git a/router.go b/router.go
index 79b72a8..e0fbfbf 100644
--- a/router.go
+++ b/router.go
@@ -38,6 +38,7 @@ type Router struct {
 	apiServer         *http.Server
 	apiServerMu       sync.Mutex
 	apiServerShutdown context.CancelFunc
+	updatingConfig    bool
 }
 
 func (r *Router) addModule(moduleDecl config.ModuleConfig) error {
@@ -122,6 +123,7 @@ func NewRouter(routerConfig config.Config) (*Router, []module.ModuleError, []rou
 		ConfigChange:    make(chan config.Config, 1),
 		logger:          slog.Default().With("component", "router"),
 		runningConfig:   routerConfig,
+		updatingConfig:  false,
 	}
 	router.logger.Debug("creating")
 
@@ -318,6 +320,10 @@ func (r *Router) RunningConfig() config.Config {
 func (r *Router) UpdateConfig(newConfig config.Config) ([]module.ModuleError, []route.RouteError) {
 	r.runningConfigMu.Lock()
 	defer r.runningConfigMu.Unlock()
+	r.updatingConfig = true
+	defer func() {
+		r.updatingConfig = false
+	}()
 	oldConfig := r.runningConfig
 	r.logger.Debug("received config update", "oldConfig", oldConfig, "newConfig", newConfig)