diff --git a/packages/qr-code-scanner/README.md b/packages/qr-code-scanner/README.md
index 3d898fa7d497eed2e6f376b72a14b85bd96ce38f..ad498df57fbf88c94663f963ed2f9c8453f9f0e1 100644
--- a/packages/qr-code-scanner/README.md
+++ b/packages/qr-code-scanner/README.md
@@ -66,7 +66,7 @@ You can use your desktop as a camera, to test the qr code reader
 sudo apt install ffmpeg v4l2loopback-dkms; sudo modprobe v4l2loopback
 
 #start virtual cam - Dummy video device (0x0000)
-ffmpeg -f x11grab -r 15 -s 1280x720 -i :0.0+0,0 -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0
+ffmpeg -f x11grab -r 15 -s 1280x720 -i "${DISPLAY}+0,0" -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0
 ```
 
 Then you can place a QR Code in the left corner of your desktop.