diff --git a/lib/attr.c b/lib/attr.c
index 298fbb1..8394330 100644
--- a/lib/attr.c
+++ b/lib/attr.c
@@ -800,6 +800,9 @@
 	struct nlattr *nla;
 	int tlen;
 	
+	if (attrlen < 0)
+		return NULL;
+
 	tlen = NLMSG_ALIGN(msg->nm_nlh->nlmsg_len) + nla_total_size(attrlen);
 
 	if ((tlen + msg->nm_nlh->nlmsg_len) > msg->nm_size)
@@ -838,6 +841,9 @@
 {
 	struct nlattr *nla;
 
+	if (datalen < 0)
+		return -NLE_RANGE;
+
 	nla = nla_reserve(msg, attrtype, datalen);
 	if (!nla)
 		return -NLE_NOMEM;