diff --git a/include/mbedtls/md5.h b/include/mbedtls/md5.h
index 4c95090..6c3354f 100644
--- a/include/mbedtls/md5.h
+++ b/include/mbedtls/md5.h
@@ -37,6 +37,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+/* MBEDTLS_ERR_MD5_HW_ACCEL_FAILED is deprecated and should not be used. */
 #define MBEDTLS_ERR_MD5_HW_ACCEL_FAILED                   -0x002F  /**< MD5 hardware accelerator failed */
 
 #ifdef __cplusplus