diff --git a/Lib/lib-tk/Tkinter.py b/Lib/lib-tk/Tkinter.py
index f8366cb934f..746adf1644f 100644
--- a/Lib/lib-tk/Tkinter.py
+++ b/Lib/lib-tk/Tkinter.py
@@ -1478,7 +1478,7 @@ def __init__(self, screenName=None, baseName=None, className='Tk'):
             if ext not in ('.py', '.pyc', '.pyo'):
                 baseName = baseName + ext
         self.tk = _tkinter.create(screenName, baseName, className)
-        if _MacOS and hasattr(MacOS, 'SchedParams'):
+        if _MacOS and hasattr(_MacOS, 'SchedParams'):
             # Disable event scanning except for Command-Period
             _MacOS.SchedParams(1, 0)
             # Work around nasty MacTk bug