diff --git a/tests/unit/test_slide.py b/tests/unit/test_slide.py
index 5db0e275..05814a5c 100644
--- a/tests/unit/test_slide.py
+++ b/tests/unit/test_slide.py
@@ -447,8 +447,8 @@ def it_knows_its_biggest_tissue_box_mask(
             request, "histolab.slide.regions_from_binary_mask"
         )
         regions_from_binary_mask.return_value = regions
-        biggest_regions_ = function_mock(
-            request, "histolab.slide.Slide._biggest_regions", autospec=False
+        biggest_regions_ = method_mock(
+            request, Slide, "_biggest_regions", autospec=False
         )
         biggest_regions_.return_value = regions
         region_coordinates_ = function_mock(