diff --git a/include/mbedtls/xtea.h b/include/mbedtls/xtea.h
index 1d01e56..34ccee3 100644
--- a/include/mbedtls/xtea.h
+++ b/include/mbedtls/xtea.h
@@ -37,6 +37,7 @@
 #define MBEDTLS_XTEA_DECRYPT     0
 
 #define MBEDTLS_ERR_XTEA_INVALID_INPUT_LENGTH             -0x0028  /**< The data input has an invalid length. */
+#define MBEDTLS_ERR_XTEA_HW_ACCEL_FAILED                  -0x0029  /**< XTEA hardware accelerator failed. */
 
 #if !defined(MBEDTLS_XTEA_ALT)
 // Regular implementation