diff --git a/src/calibre/srv/code.py b/src/calibre/srv/code.py
index cc61d72e6e..806577d525 100644
--- a/src/calibre/srv/code.py
+++ b/src/calibre/srv/code.py
@@ -4,7 +4,6 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-import cPickle
 import hashlib
 import random
 import shutil
@@ -29,6 +28,7 @@ from calibre.utils.config import prefs, tweaks
 from calibre.utils.icu import sort_key, numeric_sort_key
 from calibre.utils.localization import get_lang, lang_map_for_ui, localize_website_link
 from calibre.utils.search_query_parser import ParseException
+from calibre.utils.serialize import json_dumps
 
 POSTABLE = frozenset({'GET', 'POST', 'HEAD'})
 
@@ -382,9 +382,9 @@ def tag_browser(ctx, rd):
               &collapse_at=25&dont_collapse=&hide_empty_categories=&vl=''
     '''
     db, library_id = get_library_data(ctx, rd)[:2]
-    opts = categories_settings(rd.query, db)
+    opts = categories_settings(rd.query, db, gst_container=tuple)
     vl = rd.query.get('vl') or ''
-    etag = cPickle.dumps([db.last_modified().isoformat(), rd.username, library_id, vl, list(opts)], -1)
+    etag = json_dumps([db.last_modified().isoformat(), rd.username, library_id, vl, list(opts)])
     etag = hashlib.sha1(etag).hexdigest()
 
     def generate():
diff --git a/src/calibre/srv/metadata.py b/src/calibre/srv/metadata.py
index 9db376d257..ec2d768a9f 100644
--- a/src/calibre/srv/metadata.py
+++ b/src/calibre/srv/metadata.py
@@ -192,7 +192,7 @@ def icon_map():
         return _icon_map
 
 
-def categories_settings(query, db):
+def categories_settings(query, db, gst_container=GroupedSearchTerms):
     dont_collapse = frozenset(query.get('dont_collapse', '').split(','))
     partition_method = query.get('partition_method', 'first letter')
     if partition_method not in {'first letter', 'disable', 'partition'}:
@@ -214,7 +214,7 @@ def categories_settings(query, db):
     hidden_categories = frozenset(db.pref('tag_browser_hidden_categories', set()))
     return CategoriesSettings(
         dont_collapse, collapse_model, collapse_at, sort_by, template,
-        using_hierarchy, GroupedSearchTerms(db.pref('grouped_search_terms', {})),
+        using_hierarchy, gst_container(db.pref('grouped_search_terms', {})),
         hidden_categories, query.get('hide_empty_categories') == 'yes')