diff --git a/ext/enchant-wdk/src/makefile.mak b/ext/enchant-wdk/src/makefile.mak
index 4273b6b5..77925ad6 100644
--- a/ext/enchant-wdk/src/makefile.mak
+++ b/ext/enchant-wdk/src/makefile.mak
@@ -153,6 +153,7 @@ INCLUDES = \
 !ifdef X64
 LINKOBJ = msvcrt_win2003.obj
 MACHINE_FLAG = X64
+CFLAGS = $(CFLAGS) /favor:AMD64 /D_WIN64
 !else
 MACHINE_FLAG = X86
 LINKOBJ = msvcrt_winxp.obj