diff --git a/src/calibre/gui2/tweak_book/boss.py b/src/calibre/gui2/tweak_book/boss.py
index 9384dd9b94..3e4cb85c25 100644
--- a/src/calibre/gui2/tweak_book/boss.py
+++ b/src/calibre/gui2/tweak_book/boss.py
@@ -120,6 +120,7 @@ class Boss(QObject):
         if p.exec_() == p.Accepted:
             if p.dictionaries_changed:
                 dictionaries.clear_caches()
+                dictionaries.initialize(force=True)  # Reread user dictionaries
             for ed in editors.itervalues():
                 ed.apply_settings(dictionaries_changed=p.dictionaries_changed)
             setup_cssutils_serialization()
diff --git a/src/calibre/spell/dictionary.py b/src/calibre/spell/dictionary.py
index 2102d9daa4..0bc8220e1d 100644
--- a/src/calibre/spell/dictionary.py
+++ b/src/calibre/spell/dictionary.py
@@ -184,8 +184,8 @@ class Dictionaries(object):
             self.default_locale = parse_lang_code('en-US')
         self.ui_locale = self.default_locale
 
-    def initialize(self):
-        if not hasattr(self, 'active_user_dictionaries'):
+    def initialize(self, force=False):
+        if force or not hasattr(self, 'active_user_dictionaries'):
             self.read_user_dictionaries()
 
     def clear_caches(self):