diff --git a/extensions/adblock.c b/extensions/adblock.c
index 5ffc3c5c..9cf7931e 100644
--- a/extensions/adblock.c
+++ b/extensions/adblock.c
@@ -172,8 +172,8 @@ adblock_preferences_model_row_changed_cb (GtkTreeModel*    model,
                 g_free (filter);
         }
         while (gtk_tree_model_iter_next (model, iter));
-    filters[length] = NULL;
-    midori_extension_set_string_list (extension, "filters", filters, length);
+    filters[i] = NULL;
+    midori_extension_set_string_list (extension, "filters", filters, i);
     g_free (filters);
     if (need_reload)
         adblock_reload_rules (extension);