diff --git a/sys/boot/alpha/libalpha/Makefile b/sys/boot/alpha/libalpha/Makefile
index 702f6d519ef..0abacda9273 100644
--- a/sys/boot/alpha/libalpha/Makefile
+++ b/sys/boot/alpha/libalpha/Makefile
@@ -7,7 +7,7 @@ INTERNALLIB=	true
 
 # XXX hack to pick up stand.h
 LIBSTANDDIR=	${.CURDIR}/../../../../lib/libstand
-CFLAGS=		-I${LIBSTANDDIR}
+CFLAGS+=	-I${LIBSTANDDIR}
 CFLAGS+=	-DDEBUG
 
 # Pick up the bootstrap header for some interface items
diff --git a/sys/boot/arc/lib/Makefile b/sys/boot/arc/lib/Makefile
index a9c0e2d246c..1c7bb6cbde2 100644
--- a/sys/boot/arc/lib/Makefile
+++ b/sys/boot/arc/lib/Makefile
@@ -8,7 +8,7 @@ INTERNALLIB=	true
 .PATH:		${.CURDIR}/arch/${MACHINE_ARCH}
 # XXX hack to pick up stand.h
 LIBSTANDDIR=	${.CURDIR}/../../../../lib/libstand
-CFLAGS=		-I${LIBSTANDDIR}
+CFLAGS+=	-I${LIBSTANDDIR}
 CFLAGS+=	-DDEBUG
 
 # Pick up the bootstrap header for some interface items