diff --git a/test_autocti/extract/two_d/serial/test_serial_eper.py b/test_autocti/extract/two_d/serial/test_serial_eper.py
index aa82999c..790a24cd 100644
--- a/test_autocti/extract/two_d/serial/test_serial_eper.py
+++ b/test_autocti/extract/two_d/serial/test_serial_eper.py
@@ -1,6 +1,8 @@
 import numpy as np
+import pytest
 
 import autocti as ac
+from autocti import exc
 
 
 def test__region_list_from__array_2d_list_from(serial_array, serial_masked_array):
@@ -61,12 +63,23 @@ def test__region_list_from__array_2d_list_from(serial_array, serial_masked_array
     assert (array_2d_list[0] == np.array([[5.0], [5.0], [5.0]])).all()
     assert (array_2d_list[1] == np.array([[9.0], [9.0], [9.0]])).all()
 
-    array_2d_list = extract.array_2d_list_from(
-        array=serial_array, settings=ac.SettingsExtract(pixels=(2, 3))
-    )
-
-    assert (array_2d_list[0] == np.array([[6.0], [6.0], [6.0]])).all()
-    assert (array_2d_list[1] == np.array([[10.0], [10.0], [10.0]])).all()
+    # `pixels=(2, 3)` asks for the third column of each trailing region. For the
+    # second region (its trailing region starts at column 8) that is columns
+    # 10-11 of a 10-column array: a window entirely past the edge, which extracts
+    # to a zero-width (3, 0) structure. PyAutoArray rejects that outright, so the
+    # whole call raises rather than returning an empty extraction.
+    #
+    # This case previously asserted `array_2d_list[1] == [[10.0], [10.0], [10.0]]`
+    # and "passed" while checking nothing: comparing an empty array against
+    # anything is vacuously True, and 10.0 is not a value this fixture even
+    # contains. The behaviour is pinned here instead of left silent.
+    #
+    # A *partially* overlapping window still clips rather than raising — the
+    # `pixels=(0, 3)` case below asserts exactly that for the same region.
+    with pytest.raises(exc.MaskException):
+        extract.array_2d_list_from(
+            array=serial_array, settings=ac.SettingsExtract(pixels=(2, 3))
+        )
 
     array_2d_list = extract.array_2d_list_from(
         array=serial_array, settings=ac.SettingsExtract(pixels=(0, 3))