diff --git a/plugins/USBPrinting/USBPrinterManager.py b/plugins/USBPrinting/USBPrinterManager.py
index d2168b523b..1249c454ff 100644
--- a/plugins/USBPrinting/USBPrinterManager.py
+++ b/plugins/USBPrinting/USBPrinterManager.py
@@ -84,6 +84,7 @@ class USBPrinterManager(QObject, SignalEmitter, OutputDevicePlugin, Extension):
 
         self._firmware_view.show()
 
+    @pyqtSlot()
     def updateAllFirmware(self):
         self.spawnFirmwareInterface("")
         for printer_connection in self._printer_connections:
diff --git a/resources/qml/WizardPages/UpgradeFirmware.qml b/resources/qml/WizardPages/UpgradeFirmware.qml
index 1e91ea2468..f7031febe3 100644
--- a/resources/qml/WizardPages/UpgradeFirmware.qml
+++ b/resources/qml/WizardPages/UpgradeFirmware.qml
@@ -62,9 +62,7 @@ Item
             anchors.top: parent.top
             anchors.left: parent.left
             text: catalog.i18nc("@action:button","Upgrade to Marlin Firmware");
-            onClicked: {
-                printer_connection.updateAllFirmware
-            }
+            onClicked: UM.USBPrinterManager.updateAllFirmware()
         }
         Button {
             id: skipUpgradeButton