Check index >= 0 as 0 is a valid index.
@@ -1601,7 +1601,7 @@ int tls1_process_sigalgs(SSL *s)
if (SSL_IS_TLS13(s) && sigptr->sig == EVP_PKEY_RSA)
continue;
idx = tls12_get_pkey_idx(sigptr->sig);
- if (idx > 0 && pmd[idx] == NULL) {
+ if (idx >= 0 && pmd[idx] == NULL) {
md = ssl_md(sigptr->hash_idx);
pmd[idx] = md;
pvalid[idx] = CERT_PKEY_EXPLICIT_SIGN;
