diff --git a/lib/active_scaffold/helpers/association_helpers.rb b/lib/active_scaffold/helpers/association_helpers.rb
index <HASH>..<HASH> 100644
--- a/lib/active_scaffold/helpers/association_helpers.rb
+++ b/lib/active_scaffold/helpers/association_helpers.rb
@@ -92,7 +92,7 @@ module ActiveScaffold
         case association.macro
           when :has_one, :has_many
             # Find only orphaned objects
-            "#{association.foreign_key} IS NULL"
+            {association.foreign_key => nil}
           when :belongs_to, :has_and_belongs_to_many
             # Find all
             nil
use hash in default association options, in case foreign key needs be quoted