diff --git a/usr.sbin/traceroute6/traceroute6.c b/usr.sbin/traceroute6/traceroute6.c
index 3f116dc3d18..d9dbb40d359 100644
--- a/usr.sbin/traceroute6/traceroute6.c
+++ b/usr.sbin/traceroute6/traceroute6.c
@@ -342,7 +342,7 @@ struct ip6_rthdr *rth;
 #endif
 struct cmsghdr *cmsg;
 
-char *source = 0;
+char *source = NULL;
 char *hostname;
 
 u_long nprobes = 3;