diff --git a/tests/test_1model_class.py b/tests/test_1model_class.py
index f0d09b5f..fcdd80fc 100644
--- a/tests/test_1model_class.py
+++ b/tests/test_1model_class.py
@@ -250,6 +250,11 @@ def test_storage_volume(tmpdir):
 
     assert np.isclose(mod.grid["vol"].sum(), 34.5)
 
+    # check index of the point with maximum volume
+    index = mod.grid["vol"].argmax()
+    assert index == 1601
+
+
 def test_observations(tmpdir):
     root = TESTMODELDIR
     mod = SfincsModel(root=root, mode="r+")