diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 372bf84..15731ca 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -963,7 +963,7 @@
 
         MBEDTLS_SSL_DEBUG_BUF(3, "verify hash", verify_hash, verify_hash_len);
 
-        if ((ret = mbedtls_pk_sign_ext(pk_type, own_key,
+        if ((ret = mbedtls_pk_sign_ext((mbedtls_pk_sigalg_t) pk_type, own_key,
                                        md_alg, verify_hash, verify_hash_len,
                                        p + 4, (size_t) (end - (p + 4)), &signature_len)) != 0) {
             MBEDTLS_SSL_DEBUG_MSG(2, ("CertificateVerify signature failed with %s",