diff --git a/jax_cfd/spectral/utils.py b/jax_cfd/spectral/utils.py
index 97a6b49..4cc9cad 100644
--- a/jax_cfd/spectral/utils.py
+++ b/jax_cfd/spectral/utils.py
@@ -129,8 +129,8 @@ def brick_wall_filter_2d(grid: grids.Grid):
   """Implements the 2/3 rule."""
   n, m = grid.shape
   filter_ = jnp.zeros((n, m // 2 + 1))
-  filter_ = filter_.at[:int(2 / 3 * n) // 2, :int(2 / 3 * (m // 2 + 1))].set(1)
-  filter_ = filter_.at[-int(2 / 3 * n) // 2:, :int(2 / 3 * (m // 2 + 1))].set(1)
+  filter_ = filter_.at[:(int(2 / 3 * n) // 2 + 1), :int(2 / 3 * (m // 2 + 1))].set(1)
+  filter_ = filter_.at[-(int(2 / 3 * n) // 2):, :int(2 / 3 * (m // 2 + 1))].set(1)
   return filter_