diff --git a/include/polarssl/ecdsa.h b/include/polarssl/ecdsa.h
index a718c0e..0fab07e 100644
--- a/include/polarssl/ecdsa.h
+++ b/include/polarssl/ecdsa.h
@@ -137,6 +137,34 @@
                            int (*f_rng)(void *, unsigned char *, size_t),
                            void *p_rng );
 
+#if defined(POLARSSL_ECDSA_DETERMINISTIC)
+/**
+ * \brief           Compute ECDSA signature and write it to buffer,
+ *                  serialized as defined in RFC 4492 page 20.
+ *                  Deterministic version, RFC 6979.
+ *                  (Not thread-safe to use same context in multiple threads)
+ *
+ * \param ctx       ECDSA context
+ * \param hash      Message hash
+ * \param hlen      Length of hash
+ * \param sig       Buffer that will hold the signature
+ * \param slen      Length of the signature written
+ * \param md_alg    MD algorithm used to hash the message
+ *
+ * \note            The "sig" buffer must be at least as large as twice the
+ *                  size of the curve used, plus 7 (eg. 71 bytes if a 256-bit
+ *                  curve is used).
+ *
+ * \return          0 if successful,
+ *                  or a POLARSSL_ERR_ECP, POLARSSL_ERR_MPI or
+ *                  POLARSSL_ERR_ASN1 error code
+ */
+int ecdsa_write_signature_det( ecdsa_context *ctx,
+                               const unsigned char *hash, size_t hlen,
+                               unsigned char *sig, size_t *slen,
+                               md_type_t md_alg );
+#endif
+
 /**
  * \brief           Read and verify an ECDSA signature
  *