diff --git a/ripd/ripd.c b/ripd/ripd.c
index 90dc7808eb..fa1188d625 100644
--- a/ripd/ripd.c
+++ b/ripd/ripd.c
@@ -902,7 +902,7 @@ static int rip_auth_md5(struct rip_packet *packet, struct sockaddr_in *from,
 			return 0;
 
 		key = key_lookup_for_accept(keychain, md5->keyid);
-		if (key == NULL)
+		if (key == NULL || key->string == NULL)
 			return 0;
 
 		strncpy(auth_str, key->string, RIP_AUTH_MD5_SIZE);