diff --git a/library/bignum.c b/library/bignum.c
index d2284a4b70..5c171a0ede 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -2245,7 +2245,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
         /* This should be a no-op because W[1] is already that large before
          * mbedtls_mpi_mod_mpi(), but it's necessary to avoid an overflow
          * in mpi_montmul() below, so let's make sure. */
-        MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[1], N->n +1 ) );
+        MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[1], N->n + 1 ) );
     }
     else
         MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[1], A ) );