diff --git a/docs/api/ipc-main.md b/docs/api/ipc-main.md
index 9133b43bd3..f5cd7db8ae 100644
--- a/docs/api/ipc-main.md
+++ b/docs/api/ipc-main.md
@@ -40,6 +40,8 @@ ipcMain.on('synchronous-message', (event, arg) => {
 
 ```javascript
 // In renderer process (web page).
+// NB. Electron APIs are only accessible from preload, unless contextIsolation is disabled.
+// See https://www.electronjs.org/docs/tutorial/process-model#preload-scripts for more details.
 const { ipcRenderer } = require('electron')
 console.log(ipcRenderer.sendSync('synchronous-message', 'ping')) // prints "pong"