diff --git a/plugins/USBPrinting/USBPrinterOutputDevice.py b/plugins/USBPrinting/USBPrinterOutputDevice.py
index cf07b98ca1..6be3827e5e 100644
--- a/plugins/USBPrinting/USBPrinterOutputDevice.py
+++ b/plugins/USBPrinting/USBPrinterOutputDevice.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2019 Ultimaker B.V.
+# Copyright (c) 2020 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 
 import os
@@ -367,11 +367,18 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
         self._sendCommand("M84")
 
     def _sendNextGcodeLine(self):
-        if self._gcode_position >= len(self._gcode):
+        """
+        Send the next line of g-code, at the current `_gcode_position`, via a
+        serial port to the printer.
+
+        If the print is done, this sets `_is_printing` to `False` as well.
+        """
+        try:
+            line = self._gcode[self._gcode_position]
+        except IndexError:  # End of print, or print got cancelled.
             self._printers[0].updateActivePrintJob(None)
             self._is_printing = False
             return
-        line = self._gcode[self._gcode_position]
 
         if ";" in line:
             line = line[:line.find(";")]
@@ -401,7 +408,7 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
         if print_job is None:
             controller = GenericOutputController(self)
             controller.setCanUpdateFirmware(True)
-            print_job = PrintJobOutputModel(output_controller=controller, name=CuraApplication.getInstance().getPrintInformation().jobName)
+            print_job = PrintJobOutputModel(output_controller = controller, name = CuraApplication.getInstance().getPrintInformation().jobName)
             print_job.updateState("printing")
             self._printers[0].updateActivePrintJob(print_job)