diff --git a/Lib/importlib/test/extension/test_case_sensitivity.py b/Lib/importlib/test/extension/test_case_sensitivity.py
index c566b23..575bf69 100644
--- a/Lib/importlib/test/extension/test_case_sensitivity.py
+++ b/Lib/importlib/test/extension/test_case_sensitivity.py
@@ -2,9 +2,11 @@
 from test import support as test_support
 import unittest
 import importlib
+from .. import support
 from . import test_path_hook
 
 
+@support.case_insensitive_tests
 class ExtensionModuleCaseSensitivityTest(unittest.TestCase):
 
     def find_module(self):
@@ -30,8 +32,6 @@
 
 
 def test_main():
-    if sys.platform not in ('win32', 'darwin', 'cygwin'):
-        return
     test_support.run_unittest(ExtensionModuleCaseSensitivityTest)
 
 
diff --git a/Lib/importlib/test/source/test_case_sensitivity.py b/Lib/importlib/test/source/test_case_sensitivity.py
index 1a5ff2f..6649f37 100644
--- a/Lib/importlib/test/source/test_case_sensitivity.py
+++ b/Lib/importlib/test/source/test_case_sensitivity.py
@@ -7,6 +7,7 @@
 import unittest
 
 
+@support.case_insensitive_tests
 class CaseSensitivityTest(unittest.TestCase):
 
     """PEP 235 dictates that on case-preserving, case-insensitive file systems
@@ -48,8 +49,6 @@
 
 
 def test_main():
-    if sys.platform not in ('win32', 'darwin', 'cygwin'):
-        return
     test_support.run_unittest(CaseSensitivityTest)
 
 
diff --git a/Lib/importlib/test/support.py b/Lib/importlib/test/support.py
index 4e63cd1..3097811 100644
--- a/Lib/importlib/test/support.py
+++ b/Lib/importlib/test/support.py
@@ -36,6 +36,16 @@
     else:
         return fxn
 
+
+def case_insensitive_tests(class_):
+    """Class decorator that nullifies tests that require a case-insensitive
+    file system."""
+    if sys.platform not in ('win32', 'darwin', 'cygwin'):
+        return object()
+    else:
+        return class_
+
+
 @contextmanager
 def uncache(*names):
     """Uncache a module from sys.modules.