diff --git a/mercurial/win32.py b/mercurial/win32.py
--- a/mercurial/win32.py
+++ b/mercurial/win32.py
@@ -279,7 +279,7 @@ def executablepath():
     buf = ctypes.create_string_buffer(size + 1)
     len = _kernel32.GetModuleFileNameA(None, ctypes.byref(buf), size)
     if len == 0:
-        raise ctypes.WinError
+        raise ctypes.WinError()
     elif len == size:
         raise ctypes.WinError(_ERROR_INSUFFICIENT_BUFFER)
     return buf.value
@@ -289,7 +289,7 @@ def getuser():
     size = _DWORD(300)
     buf = ctypes.create_string_buffer(size.value + 1)
     if not _advapi32.GetUserNameA(ctypes.byref(buf), ctypes.byref(size)):
-        raise ctypes.WinError
+        raise ctypes.WinError()
     return buf.value
 
 _signalhandler = []
@@ -307,7 +307,7 @@ def setsignalhandler():
     h = _SIGNAL_HANDLER(handler)
     _signalhandler.append(h) # needed to prevent garbage collection
     if not _kernel32.SetConsoleCtrlHandler(h, True):
-        raise ctypes.WinError
+        raise ctypes.WinError()
 
 def hidewindow():
 
@@ -349,7 +349,7 @@ def _1stchild(pid):
     # create handle to list all processes
     ph = _kernel32.CreateToolhelp32Snapshot(_TH32CS_SNAPPROCESS, 0)
     if ph == _INVALID_HANDLE_VALUE:
-        raise ctypes.WinError
+        raise ctypes.WinError()
     try:
         r = _kernel32.Process32First(ph, ctypes.byref(pe))
         # loop over all processes
@@ -361,7 +361,7 @@ def _1stchild(pid):
     finally:
         _kernel32.CloseHandle(ph)
     if _kernel32.GetLastError() != _ERROR_NO_MORE_FILES:
-        raise ctypes.WinError
+        raise ctypes.WinError()
     return None # no child found
 
 class _tochildpid(int): # pid is _DWORD, which always matches in an int
@@ -413,7 +413,7 @@ def spawndetached(args):
         None, args, None, None, False, _CREATE_NO_WINDOW,
         env, os.getcwd(), ctypes.byref(si), ctypes.byref(pi))
     if not res:
-        raise ctypes.WinError
+        raise ctypes.WinError()
 
     # _tochildpid because the process is the child of COMSPEC
     return _tochildpid(pi.dwProcessId)