diff --git a/dictionary/ajax_lemma_view.py b/dictionary/ajax_lemma_view.py
index ff1c588..b65ff47 100644
--- a/dictionary/ajax_lemma_view.py
+++ b/dictionary/ajax_lemma_view.py
@@ -825,8 +825,12 @@ def get_sort_order(request):
 @ajax(method='get', encode_result=False)
 def filter_form(request):  
     if request.session.has_key('lemma_preview') and request.session['lemma_preview']:
+        if not request.session.has_key('filter_rules_lemma_preview'):
+            request.session['filter_rules_lemma_preview'] = default_filter_rules()
         filter_rules = request.session['filter_rules_lemma_preview']
-    else:    
+    else:
+        if not request.session.has_key('filter_rules'):
+            request.session['filter_rules'] = default_filter_rules()
         filter_rules = request.session['filter_rules']
       
     users = User.objects.none()