diff --git a/library/bignum_mod_raw.c b/library/bignum_mod_raw.c
index 2460329..01f5a44 100644
--- a/library/bignum_mod_raw.c
+++ b/library/bignum_mod_raw.c
@@ -122,13 +122,12 @@
 void mbedtls_mpi_mod_raw_add( mbedtls_mpi_uint *X,
                               mbedtls_mpi_uint const *A,
                               mbedtls_mpi_uint const *B,
-                              const mbedtls_mpi_uint *N,
-                              size_t limbs )
+                              const mbedtls_mpi_mod_modulus *N )
 {
     size_t carry, borrow = 0;
-    carry  = mbedtls_mpi_core_add( X, A, B, limbs );
-    borrow = mbedtls_mpi_core_sub( X, X, N, limbs);
-    (void) mbedtls_mpi_core_add_if( X, N, limbs, ( carry < borrow ) );
+    carry  = mbedtls_mpi_core_add( X, A, B, N->limbs );
+    borrow = mbedtls_mpi_core_sub( X, X, N->p, N->limbs );
+    (void) mbedtls_mpi_core_add_if( X, N->p, N->limbs, ( carry < borrow ) );
 }
 /* END MERGE SLOT 5 */
 
diff --git a/library/bignum_mod_raw.h b/library/bignum_mod_raw.h
index 7b82c06..d652238 100644
--- a/library/bignum_mod_raw.h
+++ b/library/bignum_mod_raw.h
@@ -162,17 +162,17 @@
  *
  * \param[out] X    The result of the modular addition.
  * \param[in] A     Little-endian presentation of the left operand. This
- *                  must be smaller than \p N.
+ *                  must be smaller than \p N, and have the same number of
+ *                  limbs.
  * \param[in] B     Little-endian presentation of the right operand. This
- *                  must be smaller than \p N.
- * \param[in] N     Little-endian presentation of the modulus.
- * \param limbs     Number of limbs of \p X, \p A, \p B and \p N.
+ *                  must be smaller than \p N, and have the same number of
+ *                  limbs.
+ * \param[in] N     The address of the modulus.
  */
 void mbedtls_mpi_mod_raw_add( mbedtls_mpi_uint *X,
                               mbedtls_mpi_uint const *A,
                               mbedtls_mpi_uint const *B,
-                              const mbedtls_mpi_uint *N,
-                              size_t limbs );
+                              const mbedtls_mpi_mod_modulus *N );
 /* END MERGE SLOT 5 */
 
 /* BEGIN MERGE SLOT 6 */