diff --git a/Changelog.draft.rst b/Changelog.draft.rst
index 2b109a3..eacfea1 100644
--- a/Changelog.draft.rst
+++ b/Changelog.draft.rst
@@ -21,6 +21,7 @@ Changes
 Bug Fixes
 ---------
 
+* Fix the offlineimap crash when invoking debug option 'thread'
 
 Pending for the next major release
 ==================================
diff --git a/offlineimap/init.py b/offlineimap/init.py
index 296b84b..287bbbf 100644
--- a/offlineimap/init.py
+++ b/offlineimap/init.py
@@ -226,8 +226,6 @@ class OfflineImap:
                 ui.add_debug(type)
                 if type.lower() == 'imap':
                     imaplib.Debug = 5
-                if type.lower() == 'thread':
-                    threading._VERBOSE = 1
 
         if options.runonce:
             # FIXME: maybe need a better
diff --git a/offlineimap/ui/UIBase.py b/offlineimap/ui/UIBase.py
index 02593e6..a1cc864 100644
--- a/offlineimap/ui/UIBase.py
+++ b/offlineimap/ui/UIBase.py
@@ -89,11 +89,14 @@ class UIBase:
                   (threading.currentThread().getName(),
                    s.getthreadaccount(s), account)
         s.threadaccounts[threading.currentThread()] = account
+        s.debug('thread', "Register new thread '%s' (account '%s')" %\
+                    (threading.currentThread().getName(), account))
 
     def unregisterthread(s, thr):
         """Recognizes a thread has exited."""
         if s.threadaccounts.has_key(thr):
             del s.threadaccounts[thr]
+        s.debug('thread', "Unregister thread '%s'" % thr.getName())
 
     def getthreadaccount(s, thr = None):
         if not thr: