diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index e8acc23..4d8c479 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -2290,4 +2290,7 @@
     mbedtls_ssl_protocol_version min_tls_version,
     mbedtls_ssl_protocol_version max_tls_version );
 
+int mbedtls_ssl_write_sig_alg_ext( mbedtls_ssl_context *ssl, unsigned char *buf,
+                                   const unsigned char *end, size_t *out_len );
+
 #endif /* ssl_misc.h */