diff --git a/tests/test_box.py b/tests/test_box.py
index c1c1ca2..d576086 100644
--- a/tests/test_box.py
+++ b/tests/test_box.py
@@ -402,7 +402,7 @@ def test_box_pass_unexpected_argument(boxclass):
     with pytest.raises(TypeError) as excinfo:
         fn(1, 2)
 
-    assert str(excinfo.value) == "fn() got an unexpected keyword argument 'd'"
+    assert "fn() got an unexpected keyword argument 'd'" in str(excinfo.value)
 
 
 def test_box_pass_keyerror(boxclass):
diff --git a/tests/test_stack.py b/tests/test_stack.py
index 725d378..10129b3 100644
--- a/tests/test_stack.py
+++ b/tests/test_stack.py
@@ -472,7 +472,7 @@ def test_box_pass_unexpected_argument(boxclass, teststack):
         with pytest.raises(TypeError) as excinfo:
             fn(1, 2)
 
-    assert str(excinfo.value) == "fn() got an unexpected keyword argument 'd'"
+    assert "fn() got an unexpected keyword argument 'd'" in str(excinfo.value)
 
 
 def test_box_pass_keyerror(boxclass, teststack):
