diff --git a/Makefile.vc b/Makefile.vc
index 412e1e7e..b36defa8 100644
--- a/Makefile.vc
+++ b/Makefile.vc
@@ -45,7 +45,7 @@ OUTDIR = $(OBJDIR)
 !ENDIF
 
 !IF "$(HAVE_AVX2)" == "1"
-CFLAGS += /DWEBP_HAVE_AVX2
+CFLAGS = $(CFLAGS) /DWEBP_HAVE_AVX2
 AVX2_FLAGS = /arch:AVX2
 !ENDIF