diff --git a/include/mbedtls/des.h b/include/mbedtls/des.h
index 7f8f27e..1752898 100644
--- a/include/mbedtls/des.h
+++ b/include/mbedtls/des.h
@@ -37,6 +37,7 @@
 #define MBEDTLS_DES_DECRYPT     0
 
 #define MBEDTLS_ERR_DES_INVALID_INPUT_LENGTH              -0x0032  /**< The data input has an invalid length. */
+#define MBEDTLS_ERR_DES_HW_ACCEL_FAILED                   -0x0033  /**< DES hardware accelerator failed. */
 
 #define MBEDTLS_DES_KEY_SIZE    8