diff --git a/IPython/core/ultratb.py b/IPython/core/ultratb.py
index 8569791..5649a78 100644
--- a/IPython/core/ultratb.py
+++ b/IPython/core/ultratb.py
@@ -239,7 +239,7 @@ class TBTools(colorable.Colorable):
         self.debugger_cls = debugger_cls or debugger.Pdb
 
         if call_pdb:
-            self.pdb = debugger_cls()
+            self.pdb = self.debugger_cls()
         else:
             self.pdb = None