diff --git a/protocol/enttec/dmx-usb-pro/pro.h b/protocol/enttec/dmx-usb-pro/pro.h
index cd8c396..a7a30f1 100644
--- a/protocol/enttec/dmx-usb-pro/pro.h
+++ b/protocol/enttec/dmx-usb-pro/pro.h
@@ -43,7 +43,7 @@ const uint8_t END_DELIMITER = 0xe7;         //!< End of message delimiter
  * \cite DMXUSBPro The Widget firmware version identifies the set of application messages that
  * are supported by the firmware. The Widget will ignore any unsupported application messages.
  */
-enum FIRMWARE_TYPE {
+enum FIRMWARE_TYPE : uint8_t {
   FwUnknown = 0,
   FwDMX     = 1,                            //!< Normal DMX firmware.
   FwRDM     = 2,                            //!< RDM firmware
@@ -54,7 +54,7 @@ enum FIRMWARE_TYPE {
 /**
  * @brief All message labels from API 1.44
  */
-enum MESSAGE_LABEL {
+enum MESSAGE_LABEL : uint8_t {
   OpNoop                = 0,                //!< null message, out-of-spec definition.  Not in API!
   OpReprogramFirmware   = 1,                //!< Reprogram Firmware Request
   OpProgramFlashPage    = 2,                //!< Program Flash Page Request / Reply