diff --git a/library/bignum.c b/library/bignum.c
index 176b648..d57e88e 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -2162,7 +2162,7 @@
     for( size_t i = 0; i < T_size; i++ )
     {
         MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_assign( R, &T[i],
-                                        mbedtls_mpi_cf_bool_eq( i, idx ) ) );
+                        (unsigned char) mbedtls_mpi_cf_bool_eq( i, idx ) ) );
     }
 
 cleanup:
@@ -2346,7 +2346,7 @@
             /*
              * X = X * W[wbits] R^-1 mod N
              */
-            MBEDTLS_MPI_CHK( mpi_select( &WW, W, 1 << wsize, wbits ) );
+            MBEDTLS_MPI_CHK( mpi_select( &WW, W, (size_t) 1 << wsize, wbits ) );
             mpi_montmul( X, &WW, N, mm, &T );
 
             state--;