diff --git a/extensions/chaeo/models.py b/extensions/chaeo/models.py
index dc2c9cf04bd23766b2e1d51feaab610270f9fc1f..d677d1f4191925e30a11f219957a14e786221afb 100644
--- a/extensions/chaeo/models.py
+++ b/extensions/chaeo/models.py
@@ -80,7 +80,7 @@ def generate_ilastik_object_classifier(
     labels = []
     for ii in range(0, label_stack.count):
         unique = np.unique(label_stack.iat(ii))
-        assert len(unique) >= 2, 'Label image contains more than one non-zero value'
+        assert len(unique) <= 2, 'Label image contains more than one non-zero value'
         assert unique[0] == 0, 'Label image does not contain unlabeled background'
         assert unique[-1] < len(label_names) + 1, f'Label ID {unique[-1]} exceeds number of label names: {len(label_names)}'
         labels.append(unique[-1])