diff --git a/cmd/tailscale/cli/web.go b/cmd/tailscale/cli/web.go
index 399ad05e9..bf89e096e 100644
--- a/cmd/tailscale/cli/web.go
+++ b/cmd/tailscale/cli/web.go
@@ -375,7 +375,7 @@ type mi map[string]interface{
 			data.AdvertiseExitNode = true
 		} else {
 			if data.AdvertiseRoutes != "" {
-				data.AdvertiseRoutes = ","
+				data.AdvertiseRoutes += ","
 			}
 			data.AdvertiseRoutes += r.String()
 		}