diff --git a/include/mbedtls/cmac.h b/include/mbedtls/cmac.h
index a4fd552..c196793 100644
--- a/include/mbedtls/cmac.h
+++ b/include/mbedtls/cmac.h
@@ -34,6 +34,7 @@
 extern "C" {
 #endif
 
+/* MBEDTLS_ERR_CMAC_HW_ACCEL_FAILED is deprecated and should not be used. */
 #define MBEDTLS_ERR_CMAC_HW_ACCEL_FAILED -0x007A  /**< CMAC hardware accelerator failed. */
 
 #define MBEDTLS_AES_BLOCK_SIZE          16