diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 065336b..48d0a03 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -2731,7 +2731,7 @@
 /*
  * Handshake layer functions
  */
-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)
 {
     /*