diff --git a/Tools/setup/arch.sh b/Tools/setup/arch.sh
index fd1f898237..e4084dc05b 100644
--- a/Tools/setup/arch.sh
+++ b/Tools/setup/arch.sh
@@ -81,8 +81,10 @@ if [[ $INSTALL_NUTTX == "true" ]]; then
 		vim \
 		;
 
-	# add user to uucp group (to get serial port access)
-	sudo usermod -aG uucp $USER
+	if [ ! -z "$USER" ]; then
+		# add user to dialout group (serial port access)
+		sudo usermod -aG uucp $USER
+	fi
 
 	# remove modem manager (interferes with PX4 serial port usage)
 	sudo pacman -R modemmanager --noconfirm
diff --git a/Tools/setup/ubuntu.sh b/Tools/setup/ubuntu.sh
index e25861b8d0..83e848ebb0 100755
--- a/Tools/setup/ubuntu.sh
+++ b/Tools/setup/ubuntu.sh
@@ -131,8 +131,10 @@ if [[ $INSTALL_NUTTX == "true" ]]; then
 		vim-common \
 		;
 
-	# add user to dialout group (serial port access)
-	sudo usermod -a -G dialout $USER
+	if [ ! -z "$USER" ]; then
+		# add user to dialout group (serial port access)
+		sudo usermod -a -G dialout $USER
+	fi
 
 	# Remove modem manager (interferes with PX4 serial port/USB serial usage).
 	sudo apt-get remove modemmanager -y