diff --git a/Lib/exceptions.py b/Lib/exceptions.py
index 56eed92..b785a7c 100644
--- a/Lib/exceptions.py
+++ b/Lib/exceptions.py
@@ -33,6 +33,8 @@
       |    |
       |    +-- IOError
       |    +-- OSError(*)
+      |         |
+      |         +-- WindowsError(*)
       |
       +-- EOFError
       +-- RuntimeError
@@ -139,6 +141,10 @@
     """OS system call failed."""
     pass
 
+class WindowsError(OSError):
+    """MS-Windows OS system call failed."""
+    pass
+
 class RuntimeError(StandardError):
     """Unspecified run-time error."""
     pass