--- a/src/units.hpp
+++ b/src/units.hpp
@@ -370,7 +370,7 @@
 }
 
 namespace BoardSide {
-enum BoardSide {
+enum BoardSide : int {
   AUTO,
   FRONT,
   BACK
@@ -433,7 +433,7 @@
 } // namespace Software
 
 namespace MillFeedDirection {
-enum MillFeedDirection {
+enum MillFeedDirection : int {
   ANY,
   CLIMB,
   CONVENTIONAL