diff --git a/NetworkPrinterOutputDevice.py b/NetworkPrinterOutputDevice.py
index 619a70a952..f674930dc8 100644
--- a/NetworkPrinterOutputDevice.py
+++ b/NetworkPrinterOutputDevice.py
@@ -68,12 +68,12 @@ class NetworkPrinterOutputDevice(PrinterOutputDevice):
         #        "extruders": [
         #            {
         #                "feeder": {"max_speed": 45.0, "jerk": 5.0, "acceleration": 3000.0},
-        #                "active_material": {"GUID": "xxxxxxx", "length_remaining": -1.0},
+        #                "active_material": {"guid": "xxxxxxx", "length_remaining": -1.0},
         #                "hotend": {"temperature": {"target": 0.0, "current": 22.8}, "id": "AA 0.4"}
         #            },
         #            {
         #                "feeder": {"max_speed": 45.0, "jerk": 5.0, "acceleration": 3000.0},
-        #                "active_material": {"GUID": "xxxx", "length_remaining": -1.0},
+        #                "active_material": {"guid": "xxxx", "length_remaining": -1.0},
         #                "hotend": {"temperature": {"target": 0.0, "current": 22.8}, "id": "BB 0.4"}
         #            }
         #        ],
@@ -421,7 +421,7 @@ class NetworkPrinterOutputDevice(PrinterOutputDevice):
             temperature = self._json_printer_state["heads"][0]["extruders"][index]["hotend"]["temperature"]["current"]
             self._setHotendTemperature(index, temperature)
             try:
-                material_id = self._json_printer_state["heads"][0]["extruders"][index]["active_material"]["GUID"]
+                material_id = self._json_printer_state["heads"][0]["extruders"][index]["active_material"]["guid"]
             except KeyError:
                 material_id = ""
             self._setMaterialId(index, material_id)
@@ -504,7 +504,7 @@ class NetworkPrinterOutputDevice(PrinterOutputDevice):
                         i18n_catalog.i18nc("@info:status", "Unable to start a new print job. No PrinterCore loaded in slot {0}".format(index + 1)))
                     self._error_message.show()
                     return
-                if self._json_printer_state["heads"][0]["extruders"][index]["active_material"]["GUID"] == "":
+                if self._json_printer_state["heads"][0]["extruders"][index]["active_material"]["guid"] == "":
                     Logger.log("e", "No material loaded in slot %s, unable to start print", index + 1)
                     self._error_message = Message(
                         i18n_catalog.i18nc("@info:status",
@@ -533,7 +533,7 @@ class NetworkPrinterOutputDevice(PrinterOutputDevice):
 
                 material = extruder_manager.getExtruderStack(index).findContainer({"type": "material"})
                 if material:
-                    remote_material_guid = self._json_printer_state["heads"][0]["extruders"][index]["active_material"]["GUID"]
+                    remote_material_guid = self._json_printer_state["heads"][0]["extruders"][index]["active_material"]["guid"]
                     if material.getMetaDataEntry("GUID") != remote_material_guid:
                         Logger.log("w", "Extruder %s has a different material (%s) as Cura (%s)", index + 1,
                                    remote_material_guid,