diff --git a/toonz/sources/include/tpixel.h b/toonz/sources/include/tpixel.h
index 017c8b8..5dd25b0 100644
--- a/toonz/sources/include/tpixel.h
+++ b/toonz/sources/include/tpixel.h
@@ -53,10 +53,10 @@ public:
   Channel m, b, g, r;
 #elif defined(TNZ_MACHINE_CHANNEL_ORDER_RGBM)
   unsigned char r, g, b, m;
-#elif TNZ_MACHINE_CHANNEL_ORDER_MRGB
+#elif defined(TNZ_MACHINE_CHANNEL_ORDER_MRGB)
   Channel m, r, g, b;
 #else
-  Undefined machine order !!!!
+#error "Undefined machine order !!!!"
 #endif
 
 #ifdef MACOSX