diff --git a/Lib/StringIO.py b/Lib/StringIO.py
index 087092e..cc88e9d 100644
--- a/Lib/StringIO.py
+++ b/Lib/StringIO.py
@@ -59,7 +59,7 @@
     def isatty(self):
         if self.closed:
             raise ValueError, "I/O operation on closed file"
-        return 0
+        return False
 
     def seek(self, pos, mode = 0):
         if self.closed: