diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 50535da..82c441c 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -956,9 +956,14 @@
     # On OS X < 10.6, unsetenv() doesn't return a value (bpo-13415).
     @support.requires_mac_ver(10, 6)
     def test_unset_error(self):
-        # "=" is not allowed in a variable name
-        key = 'key='
-        self.assertRaises(OSError, os.environ.__delitem__, key)
+        if sys.platform == "win32":
+            # an environment variable is limited to 32,767 characters
+            key = 'x' * 50000
+            self.assertRaises(ValueError, os.environ.__delitem__, key)
+        else:
+            # "=" is not allowed in a variable name
+            key = 'key='
+            self.assertRaises(OSError, os.environ.__delitem__, key)
 
     def test_key_type(self):
         missing = 'missingkey'