diff --git a/meanas/test/test_fdfd.py b/meanas/test/test_fdfd.py
index 8397a45..676848a 100644
--- a/meanas/test/test_fdfd.py
+++ b/meanas/test/test_fdfd.py
@@ -30,7 +30,7 @@ def test_poynting_planes(sim):
               s[2, mask].sum(), -s[2, mz].sum()]
 
     e_dot_j = sim.e * sim.j * sim.dxes[0][0][:, None, None] * sim.dxes[0][1][None, :, None] * sim.dxes[0][2][None, None, :]
-    src_energy = -e_dot_j.real / 2
+    src_energy = -e_dot_j[:, mask].real / 2
 
     assert_close(sum(planes), (src_energy).sum())