diff --git a/src/collective/collectionfilter/baseviews.py b/src/collective/collectionfilter/baseviews.py
index 7bfa64f5..5f89208f 100644
--- a/src/collective/collectionfilter/baseviews.py
+++ b/src/collective/collectionfilter/baseviews.py
@@ -99,7 +99,7 @@ def pat_options(self):
                 "reloadURL": self.reload_url,
                 "ajaxLoad": self.ajax_load,
                 "contentSelector": self.content_selector,
-                "notifyOnly": self.notify_only
+                "notifyOnly": getattr(self, "notify_only", False)
             }
         )
 
diff --git a/src/collective/collectionfilter/filteritems.py b/src/collective/collectionfilter/filteritems.py
index 3568b167..08eb91a6 100644
--- a/src/collective/collectionfilter/filteritems.py
+++ b/src/collective/collectionfilter/filteritems.py
@@ -159,7 +159,13 @@ def get_filter_items(
     # Get index in question and the current filter value of this index, if set.
     groupby_criteria = getUtility(IGroupByCriteria).groupby
     idx = groupby_criteria[group_by]["index"]
-    current_idx_value = safe_iterable(request_params.get(idx))
+
+    # Added: use index modifier, if available
+    # This fixes e.g. boolean indices which couldn’t show the current value as selected
+    idx_mod = groupby_criteria[group_by]["index_modifier"]
+    crit = request_params.get(idx)
+    crit = idx_mod(crit) if idx_mod else safe_decode(crit)
+    current_idx_value = safe_iterable(crit)
 
     # Additive filtering is about adding other filter values of the same index.
     extra_ignores = [] if narrow_down else [idx, idx + "_operator"]