diff --git a/include/mbedtls/sha256.h b/include/mbedtls/sha256.h
index 33aff28..47a31e8 100644
--- a/include/mbedtls/sha256.h
+++ b/include/mbedtls/sha256.h
@@ -36,6 +36,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+/* MBEDTLS_ERR_SHA256_HW_ACCEL_FAILED is deprecated and should not be used. */
 #define MBEDTLS_ERR_SHA256_HW_ACCEL_FAILED                -0x0037  /**< SHA-256 hardware accelerator failed */
 
 #ifdef __cplusplus