diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 70a9740..ac03884 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1780,6 +1780,13 @@
 #define MBEDTLS_SSL_TRUNCATED_HMAC
 
 /**
+ * \def MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+ *
+ * Enable modifying the maximum I/O buffer size.
+ */
+//#define MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+
+/**
  * \def MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT
  *
  * Fallback to old (pre-2.7), non-conforming implementation of the truncated
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 1666f8c..b3c5288 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1215,6 +1215,9 @@
     int in_msgtype;             /*!< record header: message type      */
     size_t in_msglen;           /*!< record header: message length    */
     size_t in_left;             /*!< amount of data read so far       */
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len;          /*!< length of input buffer           */
+#endif
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     uint16_t in_epoch;          /*!< DTLS epoch for incoming records  */
     size_t next_record_offset;  /*!< offset of the next record in datagram
@@ -1254,6 +1257,9 @@
     int out_msgtype;            /*!< record header: message type      */
     size_t out_msglen;          /*!< record header: message length    */
     size_t out_left;            /*!< amount of data not yet written   */
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t out_buf_len;         /*!< length of output buffer          */
+#endif
 
     unsigned char cur_out_ctr[8]; /*!<  Outgoing record sequence  number. */