diff --git a/g13gui/g13gui/g13/manager.py b/g13gui/g13gui/g13/manager.py
index 02a30e2..d88fd0a 100644
--- a/g13gui/g13gui/g13/manager.py
+++ b/g13gui/g13gui/g13/manager.py
@@ -181,7 +181,8 @@ class Manager(threading.Thread):
         header[0] = 0x03
 
         self._device.write(
-            usb.util.CTRL_OUT | G13Endpoints.LCD.value, bytes(header) + buffer)
+            usb.util.CTRL_OUT | G13Endpoints.LCD.value,
+            bytes(header) + bytes(buffer))
 
     def _processCommands(self):
         while True: