diff --git a/sys/dev/raid/vinum/vinumio.c b/sys/dev/raid/vinum/vinumio.c
--- a/sys/dev/raid/vinum/vinumio.c
+++ b/sys/dev/raid/vinum/vinumio.c
@@ -415,6 +415,8 @@
 static char *
 sappend(char *txt, char *s)
 {
+    if (s == NULL)
+	return NULL;
     while ((*s++ = *txt++) != 0);
     return s - 1;
 }