diff --git a/include/mbedtls/ecdsa.h b/include/mbedtls/ecdsa.h
index 3666ffe..c0088db 100644
--- a/include/mbedtls/ecdsa.h
+++ b/include/mbedtls/ecdsa.h
@@ -236,6 +236,28 @@
 #endif /* MBEDTLS_ECDSA_DETERMINISTIC */
 
 /**
+ * \brief           Convert a signature from numbers to ASN.1
+ *
+ * \param r         First number of the signature
+ * \param s         Second number of the signature
+ * \param sig       Buffer that will hold the signature
+ * \param slen      Length of the signature written
+ * \param ssize     Size of the sig buffer
+ *
+ * \note            The size of the buffer \c ssize should be at least
+ *                  `MBEDTLS_ECDSA_MAX_SIG_LEN(grp->pbits)` bytes long if
+ *                  the signature was produced from curve \c grp,
+ *                  otherwise this function will return an error.
+ *
+ * \return          0 if successful,
+ *                  or a MBEDTLS_ERR_MPI_XXX or MBEDTLS_ERR_ASN1_XXX error code
+ *
+ */
+int ecdsa_signature_to_asn1( const mbedtls_mpi *r, const mbedtls_mpi *s,
+                             unsigned char *sig, size_t *slen,
+                             size_t ssize );
+
+/**
  * \brief           Read and verify an ECDSA signature
  *
  * \param ctx       ECDSA context