diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 6a1bfa8..b148485 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -475,6 +475,30 @@
     }
 }
 
+static void mbedtls_ssl_add_hs_hdr_to_checksum( mbedtls_ssl_context *ssl,
+                                                unsigned hs_type,
+                                                size_t total_hs_len )
+{
+    unsigned char hs_hdr[4];
+
+    /* Build HS header for checksum update. */
+    hs_hdr[0] = MBEDTLS_BYTE_0( hs_type );
+    hs_hdr[1] = MBEDTLS_BYTE_2( total_hs_len );
+    hs_hdr[2] = MBEDTLS_BYTE_1( total_hs_len );
+    hs_hdr[3] = MBEDTLS_BYTE_0( total_hs_len );
+
+    ssl->handshake->update_checksum( ssl, hs_hdr, sizeof( hs_hdr ) );
+}
+
+void mbedtls_ssl_add_hs_msg_to_checksum( mbedtls_ssl_context *ssl,
+                                         unsigned hs_type,
+                                         unsigned char const *msg,
+                                         size_t msg_len )
+{
+    mbedtls_ssl_add_hs_hdr_to_checksum( ssl, hs_type, msg_len );
+    ssl->handshake->update_checksum( ssl, msg, msg_len );
+}
+
 void mbedtls_ssl_reset_checksum( mbedtls_ssl_context *ssl )
 {
     ((void) ssl);