diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index c141e8a..e4b767b 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -220,6 +220,7 @@
 #endif /* MBEDTLS_X509_CRT_PARSE_C */
 #if defined(MBEDTLS_SSL_ASYNC_PRIVATE_C)
     void *p_async_operation_ctx;        /*!< asynchronous operation context */
+    unsigned char *out_async_start;     /*!< pointer where the asynchronous operation must write in the output buffer */
 #endif /* MBEDTLS_SSL_ASYNC_PRIVATE_C */
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)