diff --git a/src/netif/ppp/utils.c b/src/netif/ppp/utils.c
index c49c179f..d03f6c25 100644
--- a/src/netif/ppp/utils.c
+++ b/src/netif/ppp/utils.c
@@ -283,6 +283,8 @@ int ppp_vslprintf(char *buf, int buflen, char *fmt, va_list args) {
 	case 'q':		/* quoted string */
 	    quoted = c == 'q';
 	    p = va_arg(args, unsigned char *);
+	    if (p == NULL)
+		p = (unsigned char *)"<NULL>";
 	    if (fillch == '0' && prec >= 0) {
 		n = prec;
 	    } else {