diff --git a/src/escpos/printer/cups.py b/src/escpos/printer/cups.py
index 3900cc6..c7eff06 100644
--- a/src/escpos/printer/cups.py
+++ b/src/escpos/printer/cups.py
@@ -181,4 +181,4 @@ class CupsPrinter(Escpos):
         if self.pending_job:
             self.send()
         print(f"Closing CUPS connection to printer {self.printer_name}")
-        self.device = None
+        self._device = False
diff --git a/src/escpos/printer/file.py b/src/escpos/printer/file.py
index e2cdad4..9eaef9a 100644
--- a/src/escpos/printer/file.py
+++ b/src/escpos/printer/file.py
@@ -76,4 +76,4 @@ class File(Escpos):
             return
         self.device.flush()
         self.device.close()
-        self.device = None
+        self._device = False
diff --git a/src/escpos/printer/lp.py b/src/escpos/printer/lp.py
index a416082..3ccacfa 100644
--- a/src/escpos/printer/lp.py
+++ b/src/escpos/printer/lp.py
@@ -87,7 +87,7 @@ class LP(Escpos):
         if not self._device:
             return
         self.device.terminate()
-        self.device = None
+        self._device = False
 
     def flush(self):
         """End line and wait for new commands."""
diff --git a/src/escpos/printer/network.py b/src/escpos/printer/network.py
index 3a84840..a33c7ff 100644
--- a/src/escpos/printer/network.py
+++ b/src/escpos/printer/network.py
@@ -92,4 +92,4 @@ class Network(Escpos):
         except socket.error:
             pass
         self.device.close()
-        self.device = None
+        self._device = False
diff --git a/src/escpos/printer/serial.py b/src/escpos/printer/serial.py
index 0ba1610..39588c9 100644
--- a/src/escpos/printer/serial.py
+++ b/src/escpos/printer/serial.py
@@ -151,4 +151,4 @@ class Serial(Escpos):
         if self.device.is_open:
             self.device.flush()
             self.device.close()
-        self.device = None
+        self._device = False
diff --git a/src/escpos/printer/usb.py b/src/escpos/printer/usb.py
index 12766ae..3295096 100644
--- a/src/escpos/printer/usb.py
+++ b/src/escpos/printer/usb.py
@@ -156,4 +156,4 @@ class Usb(Escpos):
         if not self._device:
             return
         usb.util.dispose_resources(self.device)
-        self.device = None
+        self._device = False
diff --git a/src/escpos/printer/win32raw.py b/src/escpos/printer/win32raw.py
index 7658fc5..e7f18ab 100644
--- a/src/escpos/printer/win32raw.py
+++ b/src/escpos/printer/win32raw.py
@@ -97,7 +97,7 @@ class Win32Raw(Escpos):
         win32print.EndPagePrinter(self.device)
         win32print.EndDocPrinter(self.device)
         win32print.ClosePrinter(self.device)
-        self.device = None
+        self._device = False
 
     @dependency_win32print
     def _raw(self, msg):