diff --git a/zsnes/src/makefile.ms b/zsnes/src/makefile.ms
index ec1b436c..7b6d2008 100644
--- a/zsnes/src/makefile.ms
+++ b/zsnes/src/makefile.ms
@@ -136,8 +136,8 @@ ifeq (${DEBUG},yes)
 endif
 
 ifeq (${DEV},yes)
-  CFLAGSORIG=-D__DEVELOPER__
-  ASMFLAGSORIG=-D__DEVELOPER__
+  CFLAGSORIG+=-D__DEVELOPER__
+  ASMFLAGSORIG+=-D__DEVELOPER__
 endif
 
 ifeq (${RELEASEGRADE},yes)