diff --git a/usr.bin/kdump/Makefile b/usr.bin/kdump/Makefile
index daa288f86a0..534538fb933 100644
--- a/usr.bin/kdump/Makefile
+++ b/usr.bin/kdump/Makefile
@@ -8,6 +8,6 @@ SRCS=	kdump.c ioctl.c subr.c
 CLEANFILES+=ioctl.c
 
 ioctl.c: mkioctls
-	DESTDIR=${DESTDIR} /bin/sh ${.CURDIR}/mkioctls > ioctl.c
+	sh ${.CURDIR}/mkioctls ${DESTDIR}/usr/include > ioctl.c
 
 .include <bsd.prog.mk>
diff --git a/usr.bin/kdump/mkioctls b/usr.bin/kdump/mkioctls
index cbf2f0684a4..5c5dca967b3 100644
--- a/usr.bin/kdump/mkioctls
+++ b/usr.bin/kdump/mkioctls
@@ -2,11 +2,23 @@ set -e
 
 # $FreeBSD$
 
+if [ "x$1" = "x-s" ]; then
+	use_switch=1
+	shift
+else
+	use_switch=0
+fi
+
+if [ -z "$1" ]; then
+	echo "usage: sh $0 [-s] include-dir"
+	exit 1
+fi
+
 # Build a list of headers that have ioctls in them.
 # XXX should we use an ANSI cpp?
 # XXX netipx conflicts with netns (leave out netns).
 ioctl_includes=`
-	cd $DESTDIR/usr/include
+	cd $1
 	find * -name '*.h' -follow |
 		egrep -v '^(netns)/' |
 		xargs egrep -l \
@@ -15,8 +27,8 @@ ioctl_includes=`
 `
 
 echo "$ioctl_includes" |
-	cpp -I$DESTDIR/usr/include -dM |
-	awk -v ioctl_includes="$ioctl_includes" '
+	gcc -E -I$1 -dM - |
+	awk -v ioctl_includes="$ioctl_includes" -v use_switch="$use_switch" '
 BEGIN {
 	print "/* XXX obnoxious prerequisites. */"
 	print "#define COMPAT_43"
@@ -51,8 +63,7 @@ BEGIN {
 	print "ioctlname(register_t val)"
 	print "{"
 	print ""
-	generate_case_statement = 0
-	if (generate_case_statement)
+	if (use_switch)
 		print "\tswitch(val) {"
 }
 
@@ -64,14 +75,14 @@ BEGIN {
 			break;
 	++i;
 	# 
-	if (generate_case_statement)
+	if (use_switch)
 		printf("\tcase %s:\n\t\treturn(\"%s\");\n", $i, $i);
 	else
 		printf("\tif (val ==  %s)\n\t\treturn(\"%s\");\n", $i, $i);
 
 }
 END {
-	if (generate_case_statement)
+	if (use_switch)
 		print "\t}"
 	print "\n\treturn(NULL);"
 	print "}"