diff --git a/inarp.c b/inarp.c
index 08a0c30..4b4f03e 100644
--- a/inarp.c
+++ b/inarp.c
@@ -360,7 +360,9 @@
 		return;
 	}
 
-	for_each_nlmsg(buf, nlmsg, len)
+	size_t len_unsigned = (size_t)len;
+
+	for_each_nlmsg(buf, nlmsg, len_unsigned)
 		netlink_nlmsg(inarp, nlmsg);
 }