Break cycle on close.
diff --git a/Tools/idle/Debugger.py b/Tools/idle/Debugger.py
index b085a1d..267d39f 100644
--- a/Tools/idle/Debugger.py
+++ b/Tools/idle/Debugger.py
@@ -26,6 +26,8 @@
         if self.interacting:
             self.top.bell()
             return
+        if self.stackviewer:
+            self.stackviewer.close(); self.stackviewer = None
         self.pyshell.close_debugger()
         self.top.destroy()