--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -66,7 +66,7 @@ class ui(object):
def isatty(self):
if ui._isatty is None:
- ui._isatty = os.isatty(sys.stdin.fileno())
+ ui._isatty = sys.stdin.isatty()
return ui._isatty
def updateopts(self, verbose=False, debug=False, quiet=False,