diff -r 3ff4b07412ad -r de23a552fc23 mercurial/extensions.py
--- a/mercurial/extensions.py	Sun May 31 14:40:28 2015 +0900
+++ b/mercurial/extensions.py	Mon Mar 30 16:23:35 2015 +0900
@@ -85,6 +85,8 @@
         except ImportError, err:
             ui.debug('could not import hgext.%s (%s): trying %s\n'
                      % (name, err, name))
+            if ui.debugflag:
+                ui.traceback()
             mod = importh(name)
     _extensions[shortname] = mod
     _order.append(shortname)
@@ -110,6 +112,7 @@
             else:
                 ui.warn(_("*** failed to import extension %s: %s\n")
                         % (name, inst))
+            ui.traceback()
 
     for name in _order[newindex:]:
         uisetup = getattr(_extensions[name], 'uisetup', None)