diff --git a/include/mbedtls/xtea.h b/include/mbedtls/xtea.h
index c70c3fe..6430c13 100644
--- a/include/mbedtls/xtea.h
+++ b/include/mbedtls/xtea.h
@@ -37,6 +37,8 @@
 #define MBEDTLS_XTEA_DECRYPT     0
 
 #define MBEDTLS_ERR_XTEA_INVALID_INPUT_LENGTH             -0x0028  /**< The data input has an invalid length. */
+
+/* MBEDTLS_ERR_XTEA_HW_ACCEL_FAILED is deprecated and should not be used. */
 #define MBEDTLS_ERR_XTEA_HW_ACCEL_FAILED                  -0x0029  /**< XTEA hardware accelerator failed. */
 
 #ifdef __cplusplus