diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index c636ad4..eae192b 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -1409,7 +1409,7 @@
  * Write handshake message header
  */
 MBEDTLS_CHECK_RETURN_CRITICAL
-int mbedtls_ssl_start_handshake_msg(mbedtls_ssl_context *ssl, unsigned hs_type,
+int mbedtls_ssl_start_handshake_msg(mbedtls_ssl_context *ssl, unsigned char hs_type,
                                     unsigned char **buf, size_t *buf_len);
 
 MBEDTLS_CHECK_RETURN_CRITICAL