diff --git a/vm/Config.x86.64 b/vm/Config.x86.64
index 2d9efa40f3..ce60ae1948 100644
--- a/vm/Config.x86.64
+++ b/vm/Config.x86.64
@@ -1,3 +1,3 @@
 PLAF_DLL_OBJS += vm/cpu-x86.o
 PLAF_MASTER_HEADERS += vm/cpu-x86.hpp
-SITE_CFLAGS=-m64
+SITE_CFLAGS += -m64