diff --git a/cmdmon.c b/cmdmon.c
index 020aa26..8406087 100644
--- a/cmdmon.c
+++ b/cmdmon.c
@@ -566,6 +566,7 @@ get_more_replies(void)
     for (i=1; i<REPLY_EXTEND_QUANTUM; i++) {
       new_replies[i-1].next = new_replies + i;
     }
+    new_replies[REPLY_EXTEND_QUANTUM - 1].next = NULL;
     free_replies = new_replies;
   }
 }