diff --git a/krb5/usr.bin/ksu/Makefile b/krb5/usr.bin/ksu/Makefile
index aaec461ce0b..93860e38ce5 100644
--- a/krb5/usr.bin/ksu/Makefile
+++ b/krb5/usr.bin/ksu/Makefile
@@ -24,7 +24,8 @@ SRCS=	authorization.c \
 
 CFLAGS+=-I${KRB5_DIR}/include \
 	-I${KRB5_SRCTOP}/include \
-	-DGET_TGT_VIA_PASSWD
+	-DGET_TGT_VIA_PASSWD \
+	-DPRINC_LOOK_AHEAD
 
 MAN=	ksu.1