diff --git a/cmd/tailscale/cli/web.go b/cmd/tailscale/cli/web.go
index 67de1c29c..ecfb5c481 100644
--- a/cmd/tailscale/cli/web.go
+++ b/cmd/tailscale/cli/web.go
@@ -214,7 +214,8 @@ func webHandler(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		url, err := tailscaleUpForceReauth(r.Context())
 		if err != nil {
-			json.NewEncoder(w).Encode(mi{"error": err})
+			w.WriteHeader(500)
+			json.NewEncoder(w).Encode(mi{"error": err.Error()})
 			return
 		}
 		json.NewEncoder(w).Encode(mi{"url": url})