diff --git a/docs/deployment.md b/docs/deployment.md
index fc09ac4108fd..eb18e43310f5 100644
--- a/docs/deployment.md
+++ b/docs/deployment.md
@@ -136,7 +136,18 @@ Next.js will automatically load the latest version of your application in the ba
 
 Sometimes you might want to run some cleanup code on process signals like `SIGTERM` or `SIGINT`.
 
-You can do that by setting the env variable `NEXT_MANUAL_SIG_HANDLE` to `true` and then register a handler for that signal inside your `_document.js` file.
+You can do that by setting the env variable `NEXT_MANUAL_SIG_HANDLE` to `true` and then register a handler for that signal inside your `_document.js` file. Please note that you need to register env variable directly in the system env variable, not in the `.env` file.
+
+```json
+// package.json
+{
+  "scripts": {
+    "dev": "NEXT_MANUAL_SIG_HANDLE=true next dev",
+    "build": "next build",
+    "start": "NEXT_MANUAL_SIG_HANDLE=true next start"
+  }
+}
+```
 
 ```js
 // pages/_document.js