diff --git a/sim_serial.c b/sim_serial.c
index 0dd41cbb..f0068887 100644
--- a/sim_serial.c
+++ b/sim_serial.c
@@ -188,7 +188,7 @@ serial_open_devices[serial_open_device_count-1].port = port;
 serial_open_devices[serial_open_device_count-1].line = line;
 strncpy(serial_open_devices[serial_open_device_count-1].name, name, sizeof(serial_open_devices[serial_open_device_count-1].name)-1);
 if (config)
-    strncpy(serial_open_devices[serial_open_device_count-1].config, config, sizeof(serial_open_devices[serial_open_device_count-1].config));
+    strncpy(serial_open_devices[serial_open_device_count-1].config, config, sizeof(serial_open_devices[serial_open_device_count-1].config)-1);
 return &serial_open_devices[serial_open_device_count-1];
 }