diff --git a/sys/boot/i386/kgzldr/Makefile b/sys/boot/i386/kgzldr/Makefile
index fff828b69c1..6207f737827 100644
--- a/sys/boot/i386/kgzldr/Makefile
+++ b/sys/boot/i386/kgzldr/Makefile
@@ -11,7 +11,7 @@ LDFLAGS=-nostdlib -static -r
 .for asm in start crt sio
 OBJS+=	${asm}.o
 ${asm}.o: ${asm}.s
-	as -o ${.TARGET} ${.ALLSRC:M*${asm}*}
+	${AS} ${AFLAGS} -o ${.TARGET} ${.ALLSRC:M*${asm}*}
 .endfor
 
 CLEANFILES=kgzldr.o
diff --git a/sys/boot/i386/libi386/Makefile b/sys/boot/i386/libi386/Makefile
index 22ee1e505d4..aba477ab10c 100644
--- a/sys/boot/i386/libi386/Makefile
+++ b/sys/boot/i386/libi386/Makefile
@@ -47,6 +47,6 @@ machine:
 
 OBJS+=	pxetramp.o
 pxetramp.o: pxetramp.s
-	as -o ${.TARGET} ${.ALLSRC:M*pxetramp*}
+	${AS} ${AFLAGS} -o ${.TARGET} ${.ALLSRC:M*pxetramp*}
 
 .include <bsd.lib.mk>
diff --git a/sys/boot/pc98/kgzldr/Makefile b/sys/boot/pc98/kgzldr/Makefile
index 9fed53da63c..66e725e4f4f 100644
--- a/sys/boot/pc98/kgzldr/Makefile
+++ b/sys/boot/pc98/kgzldr/Makefile
@@ -14,7 +14,7 @@ AFLAGS+=--defsym PC98=1
 .for asm in start crt sio
 OBJS+=	${asm}.o
 ${asm}.o: ${asm}.s
-	as -o ${.TARGET} ${.ALLSRC:M*${asm}*}
+	${AS} ${AFLAGS} -o ${.TARGET} ${.ALLSRC:M*${asm}*}
 .endfor
 
 CLEANFILES=kgzldr.o
diff --git a/sys/boot/pc98/libpc98/Makefile b/sys/boot/pc98/libpc98/Makefile
index be420a43f24..5fe3f56528f 100644
--- a/sys/boot/pc98/libpc98/Makefile
+++ b/sys/boot/pc98/libpc98/Makefile
@@ -49,6 +49,6 @@ machine:
 
 OBJS+=	pxetramp.o
 pxetramp.o: pxetramp.s
-	as -o ${.TARGET} ${.ALLSRC:M*pxetramp*}
+	${AS} ${AFLAGS} -o ${.TARGET} ${.ALLSRC:M*pxetramp*}
 
 .include <bsd.lib.mk>