diff --git a/src/escpos/escpos.py b/src/escpos/escpos.py
index c6ea6bf..549bdbb 100644
--- a/src/escpos/escpos.py
+++ b/src/escpos/escpos.py
@@ -142,7 +142,7 @@ class Escpos(object):
         return self._device
 
     @device.setter
-    def device(self, new_device):
+    def device(self, new_device: object):
         self._device = new_device
 
     def open(self):