diff --git a/library/bignum_mod.h b/library/bignum_mod.h
index 95aaacc..f8c71d0 100644
--- a/library/bignum_mod.h
+++ b/library/bignum_mod.h
@@ -217,6 +217,40 @@
 
 /* BEGIN MERGE SLOT 2 */
 
+/** \brief  Multiply two residues, returning the residue modulo the specified
+ *          modulus.
+ *
+ * \note Currenty handles the case when `m->int_rep` is
+ * MBEDTLS_MPI_MOD_REP_MONTGOMERY.
+ *
+ * The size of the operation is determined by \p N. \p A and \p B must have
+ * the same number of limbs as \p N.
+ *
+ * \p X may be aliased to \p A or \p B, or even both, but may not overlap
+ * either otherwise. They may not alias \p N (since they must be in canonical
+ * form, they cannot == \p N).
+ *
+ * \param[out] X        The address of the result MPI.
+ *                      This must be initialized. Must have enough limbs to
+ *                      store the full value of the result.
+ *                      On successful completion, \p X contains the result of
+ *                      the multiplication `A * B * R^-1` mod N where
+ *                      `R = 2^(biL *N->limbs)`.
+ * \param[in]  A        The address of the first MPI. This must be initialized.
+ * \param[in]  B        The address of the second MPI. This must be initialized.
+ * \param[in]  N        The address of the modulus. Used to perform a modulo
+ *                      operation on the result of the multiplication.
+ *
+ * \return      \c 0 if successful.
+ * \return      #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if all the parameters does not
+ *              have the same number of limbs or \p N is invalid.
+ * \return      #MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
+ */
+int mbedtls_mpi_mod_mul( mbedtls_mpi_mod_residue *X,
+                         const mbedtls_mpi_mod_residue *A,
+                         const mbedtls_mpi_mod_residue *B,
+                         const mbedtls_mpi_mod_modulus *N );
+
 /* END MERGE SLOT 2 */
 
 /* BEGIN MERGE SLOT 3 */