diff --git a/usr.bin/su/Makefile b/usr.bin/su/Makefile
index 25216cf44f1..0002e869c47 100644
--- a/usr.bin/su/Makefile
+++ b/usr.bin/su/Makefile
@@ -5,6 +5,8 @@
 
 PROG=	su
 
+WARNS?=	5
+
 DPADD=	${LIBUTIL} ${LIBPAM}
 LDADD=	-lutil ${MINUSLPAM}