diff --git a/usr/src/boot/userboot/userboot/Makefile b/usr/src/boot/userboot/userboot/Makefile
index c15c4ac7c9..aab5b6839d 100644
--- a/usr/src/boot/userboot/userboot/Makefile
+++ b/usr/src/boot/userboot/userboot/Makefile
@@ -75,7 +75,7 @@ SRCS=		$(OBJS_SHARED:%.o=%.c) \
 
 CSTD=		$(CSTD_GNU99)
 SRCDIR=		.
-CFLAGS64 +=	$(CSOURCEDEBUGFLAGS) -fPIC $(CSTD)
+CFLAGS64 +=	$(CSOURCEDEBUGFLAGS) -m64 -fPIC $(CSTD)
 CPPFLAGS +=	-D_STANDALONE -DLOADER_MBR_SUPPORT -DLOADER_GPT_SUPPORT
 CPPFLAGS +=	-I$(SRC)/boot/include
 CPPFLAGS +=	-I$(SRC)/boot/sys