diff --git a/package.json b/package.json
index f60ccc4d..1c208eab 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,7 @@
     "start": "node backend.js",
     "build": "npm run start",
     "test": "npm run proxy-validator",
-    "start-test-server": "set -e; node backend.js & bg_pid=$!; timeout 5 wait \"${bg_pid}\"",
+    "start-test-server": "set -e; node backend.js & bg_pid=$!; timeout 5 $(wait \"${bg_pid}\")",
     "proxy-validator": "node proxyServiceValidator.js"
   },
   "keywords": [