diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 5f15b8d..dfb5634 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -1385,6 +1385,9 @@
                                          unsigned hs_type,
                                          size_t total_hs_len );
 
+#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+int mbedtls_ssl_write_signature_algorithms_ext(mbedtls_ssl_context* ssl, unsigned char* buf, unsigned char* end, size_t* olen);
+#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
 
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */