diff --git a/README.md b/README.md
index db9a4ff..dfe6501 100644
--- a/README.md
+++ b/README.md
@@ -164,7 +164,6 @@ Tooling:
 
 Linux Systemd
 -------------
-
 First make sure 'ubxtool' has been compiled (run: make ubxtool). Then, as
 root:
 ```
@@ -189,6 +188,13 @@ systemctl start ubxtool
 
 To check if it is all working, do 'service ubxtool status'.
 
+> NOTE!  If you don't use one of the AliExpress or Navilock devices, it may
+> be that your U-blox is not connected to the USB-port of the U-blox chip
+> but to the UART1 or UART2 port.  If so, you'll need to edit the script so
+> it finds your USB-to-serial adapter.  At the very least you'll have to
+> update the DEVICE line.  You'll likely also have to add --ubxport 1 at the
+> end, and likely also the baudrate (-b) and/or --rtscts=0.
+
 To change the default constellations, create a file called
 /usr/local/ubxtool/constellations and set your favorites. To set all four
 constellations (which only F9-receivers support), do as root: