diff --git a/tests/Machines/TestVariantNode.py b/tests/Machines/TestVariantNode.py
index bc860058a1..6e3a469877 100644
--- a/tests/Machines/TestVariantNode.py
+++ b/tests/Machines/TestVariantNode.py
@@ -139,6 +139,7 @@ def test_preferredMaterialExactMatch(empty_variant_node):
         "some_different_material": MagicMock(getMetaDataEntry = lambda x: 3),
         "preferred_material_base_file": MagicMock(getMetaDataEntry = lambda x: 3)  # Exact match.
     }
+    empty_variant_node.machine.preferred_material = "preferred_material_base_file"
 
     assert empty_variant_node.preferredMaterial(approximate_diameter = 3) == empty_variant_node.materials["preferred_material_base_file"], "It should match exactly on this one since it's the preferred material."
 
@@ -149,6 +150,7 @@ def test_preferredMaterialSubmaterial(empty_variant_node):
         "some_different_material": MagicMock(getMetaDataEntry = lambda x: 3),
         "preferred_material_base_file_aa04": MagicMock(getMetaDataEntry = lambda x: 3)  # This is a submaterial of the preferred material.
     }
+    empty_variant_node.machine.preferred_material = "preferred_material_base_file_aa04"
 
     assert empty_variant_node.preferredMaterial(approximate_diameter = 3) == empty_variant_node.materials["preferred_material_base_file_aa04"], "It should match on the submaterial just as well."
 
@@ -160,6 +162,7 @@ def test_preferredMaterialDiameter(empty_variant_node):
         "preferred_material_wrong_diameter": MagicMock(getMetaDataEntry = lambda x: 2),  # Approximate diameter is 2 instead of 3.
         "preferred_material_correct_diameter": MagicMock(getMetaDataEntry = lambda x: 3)  # Correct approximate diameter.
     }
+    empty_variant_node.machine.preferred_material = "preferred_material_correct_diameter"
 
     assert empty_variant_node.preferredMaterial(approximate_diameter = 3) == empty_variant_node.materials["preferred_material_correct_diameter"], "It should match only on the material with correct diameter."