diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index 9ec33da..df3a03c 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -64,6 +64,8 @@
 #define MBEDTLS_ERR_PK_UNKNOWN_NAMED_CURVE -0x3A00  /**< Elliptic curve is unsupported (only NIST curves are supported). */
 #define MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE -0x3980  /**< Unavailable feature, e.g. RSA disabled for RSA key. */
 #define MBEDTLS_ERR_PK_SIG_LEN_MISMATCH    -0x3900  /**< The buffer contains a valid signature followed by more data. */
+
+/* MBEDTLS_ERR_PK_HW_ACCEL_FAILED is deprecated and should not be used. */
 #define MBEDTLS_ERR_PK_HW_ACCEL_FAILED     -0x3880  /**< PK hardware accelerator failed. */
 
 #ifdef __cplusplus