diff --git a/library/constant_time.c b/library/constant_time.c
index 8980701..3f324ec 100644
--- a/library/constant_time.c
+++ b/library/constant_time.c
@@ -678,22 +678,14 @@
                                   unsigned char assign )
 {
     int ret = 0;
-    size_t i;
-    mbedtls_mpi_uint limb_mask;
     MPI_VALIDATE_RET( X != NULL );
     MPI_VALIDATE_RET( Y != NULL );
 
-    /* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */
-    limb_mask = mbedtls_ct_mpi_uint_mask( assign );;
-
     MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
 
     X->s = mbedtls_ct_cond_select_sign( assign, Y->s, X->s );
 
-    mbedtls_ct_mpi_uint_cond_assign( Y->n, X->p, Y->p, assign );
-
-    for( i = Y->n; i < X->n; i++ )
-        X->p[i] &= ~limb_mask;
+    mbedtls_mpi_core_cond_assign( X->p, X->n, Y->p, Y->n, assign );
 
 cleanup:
     return( ret );
@@ -710,18 +702,12 @@
                                 unsigned char swap )
 {
     int ret, s;
-    size_t i;
-    mbedtls_mpi_uint limb_mask;
-    mbedtls_mpi_uint tmp;
     MPI_VALIDATE_RET( X != NULL );
     MPI_VALIDATE_RET( Y != NULL );
 
     if( X == Y )
         return( 0 );
 
-    /* all-bits 1 if swap is 1, all-bits 0 if swap is 0 */
-    limb_mask = mbedtls_ct_mpi_uint_mask( swap );
-
     MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_grow( Y, X->n ) );
 
@@ -729,13 +715,7 @@
     X->s = mbedtls_ct_cond_select_sign( swap, Y->s, X->s );
     Y->s = mbedtls_ct_cond_select_sign( swap, s, Y->s );
 
-
-    for( i = 0; i < X->n; i++ )
-    {
-        tmp = X->p[i];
-        X->p[i] = ( X->p[i] & ~limb_mask ) | ( Y->p[i] & limb_mask );
-        Y->p[i] = ( Y->p[i] & ~limb_mask ) | (     tmp & limb_mask );
-    }
+    mbedtls_mpi_core_cond_swap( X->p, X->n, Y->p, Y->n, swap );
 
 cleanup:
     return( ret );