diff --git a/README.md b/README.md
index af52e8c..2943682 100644
--- a/README.md
+++ b/README.md
@@ -116,7 +116,7 @@ The **mbusd** service can be started via:
 
 	# systemctl start mbusd@<serial port>.service
 
-where `<serial port>` is serial port device name (like `ttyUSB0`).
+where `<serial port>` is escaped serial port device short name (like `ttyUSB0` for `/dev/ttyUSB0` device name or `serial-rs485` for `/dev/serial/rs485` device name).
 
 **mbusd** started by systemd will read its configuration from file named `/etc/mbusd/mbusd-<serial port>.conf`.
 This way it's possible to run multiple **mbusd** instances with different configurations.
diff --git a/systemd-units/mbusd@.service.in b/systemd-units/mbusd@.service.in
index 1be74c3..4b6b0a8 100644
--- a/systemd-units/mbusd@.service.in
+++ b/systemd-units/mbusd@.service.in
@@ -5,7 +5,7 @@ After=network-online.target
 Wants=network-online.target
 
 [Service]
-ExecStart=@CMAKE_INSTALL_FULL_BINDIR@/mbusd -d -v2 -L - -c @CMAKE_INSTALL_FULL_SYSCONFDIR@/mbusd/mbusd-%i.conf -p /dev/%i
+ExecStart=@CMAKE_INSTALL_FULL_BINDIR@/mbusd -d -v2 -L - -c @CMAKE_INSTALL_FULL_SYSCONFDIR@/mbusd/mbusd-%i.conf -p /dev/%I
 Restart=on-failure
 RestartSec=1
 StandardOutput=journal