diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 17149c5..eb11f7b 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -2788,4 +2788,64 @@
 int mbedtls_ssl_tls13_finalize_client_hello(mbedtls_ssl_context *ssl);
 #endif
 
+#if defined(MBEDTLS_TEST_HOOKS) && defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC)
+
+/** Compute the HMAC of variable-length data with constant flow.
+ *
+ * This function computes the HMAC of the concatenation of \p add_data and \p
+ * data, and does with a code flow and memory access pattern that does not
+ * depend on \p data_len_secret, but only on \p min_data_len and \p
+ * max_data_len. In particular, this function always reads exactly \p
+ * max_data_len bytes from \p data.
+ *
+ * \param ctx               The HMAC context. It must have keys configured
+ *                          with mbedtls_md_hmac_starts() and use one of the
+ *                          following hashes: SHA-384, SHA-256, SHA-1 or MD-5.
+ *                          It is reset using mbedtls_md_hmac_reset() after
+ *                          the computation is complete to prepare for the
+ *                          next computation.
+ * \param add_data          The first part of the message whose HMAC is being
+ *                          calculated. This must point to a readable buffer
+ *                          of \p add_data_len bytes.
+ * \param add_data_len      The length of \p add_data in bytes.
+ * \param data              The buffer containing the second part of the
+ *                          message. This must point to a readable buffer
+ *                          of \p max_data_len bytes.
+ * \param data_len_secret   The length of the data to process in \p data.
+ *                          This must be no less than \p min_data_len and no
+ *                          greater than \p max_data_len.
+ * \param min_data_len      The minimal length of the second part of the
+ *                          message, read from \p data.
+ * \param max_data_len      The maximal length of the second part of the
+ *                          message, read from \p data.
+ * \param output            The HMAC will be written here. This must point to
+ *                          a writable buffer of sufficient size to hold the
+ *                          HMAC value.
+ *
+ * \retval 0 on success.
+ * \retval #MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED
+ *         The hardware accelerator failed.
+ */
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+int mbedtls_ct_hmac(mbedtls_svc_key_id_t key,
+                    psa_algorithm_t mac_alg,
+                    const unsigned char *add_data,
+                    size_t add_data_len,
+                    const unsigned char *data,
+                    size_t data_len_secret,
+                    size_t min_data_len,
+                    size_t max_data_len,
+                    unsigned char *output);
+#else
+int mbedtls_ct_hmac(mbedtls_md_context_t *ctx,
+                    const unsigned char *add_data,
+                    size_t add_data_len,
+                    const unsigned char *data,
+                    size_t data_len_secret,
+                    size_t min_data_len,
+                    size_t max_data_len,
+                    unsigned char *output);
+#endif /* defined(MBEDTLS_USE_PSA_CRYPTO) */
+#endif /* MBEDTLS_TEST_HOOKS && defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC) */
+
 #endif /* ssl_misc.h */