diff --git a/Lib/bdb.py b/Lib/bdb.py
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -70,7 +70,10 @@
 # XXX 'arg' is no longer used
 if self.botframe is None:
 # First call of dispatch since reset()
- self.botframe = frame.f_back # (CT) Note that this may also be None!
+ # Note that frame may be a debugger frame. The derived class must
+ # ensure that self.botframe is a debuggee frame and not a debugger
+ # frame.
+ self.botframe = frame
 return self.trace_dispatch
 if not (self.stop_here(frame) or self.break_anywhere(frame)):
 # No need to trace this function
diff --git a/Lib/pdb.py b/Lib/pdb.py
--- a/Lib/pdb.py
+++ b/Lib/pdb.py
@@ -193,9 +193,9 @@
 raise KeyboardInterrupt
 self.message("\nProgram interrupted. (Use 'cont' to resume).")
 self.set_step()
- self.set_trace(frame)
 # restore previous signal handler
 signal.signal(signal.SIGINT, self._previous_sigint_handler)
+ sys.settrace(self.trace_dispatch)
 
 def reset(self):
 bdb.Bdb.reset(self)
@@ -261,6 +261,7 @@
 if (self.mainpyfile != self.canonic(frame.f_code.co_filename)
 or frame.f_lineno <= 0):
 return
+ self.botframe = frame
 self._wait_for_mainpyfile = False
 if self.bp_commands(frame):
 self.interaction(frame, None)
</div><div class="naked_ctrl">
<form action="/index.cgi/contrast" method="get" name="gate">
<p><a href="http://altstyle.alfasado.net">AltStyle</a> によって変換されたページ <a href="https://bugs.python.org/file25489/pdb_botframe_default.patch">(-&gt;オリジナル)</a>
/ <label>アドレス: <input type="text" name="naked_post_url" value="https://bugs.python.org/file25489/pdb_botframe_default.patch" size="22" /></label> <label>モード: <select name="naked_post_mode">
<option value="default">デフォルト</option>
<option value="speech">音声ブラウザ</option>
<option value="ruby">ルビ付き</option>
<option value="contrast" selected="selected">配色反転</option>
<option value="larger-text">文字拡大</option>
<option value="mobile">モバイル</option>
</select>
<input type="submit" value="表示" />
</p>
</form>
</div>