diff --git a/test/unit/test_filters.py b/test/unit/test_filters.py
index ef03fe76b..66cbbc67f 100644
--- a/test/unit/test_filters.py
+++ b/test/unit/test_filters.py
@@ -275,7 +275,7 @@ def test_local_thickness_known_sizes(self):
         im = np.zeros(shape=[300, 300])
         im = ps.generators.random_spheres(im=im, r=20)
         im = ps.generators.random_spheres(im=im, r=10)
-        lt = ps.filters.local_thickness(~im, sizes=[20, 10])
+        lt = ps.filters.local_thickness(im, sizes=[20, 10])
         assert np.all(np.unique(lt) == [0, 10, 20])
 
     def test_porosimetry(self):