--- activerecord-3.0.3/lib/active_record/associations/through_association_scope.rb.orig	2010-12-15 19:27:30.000000000 -0200
+++ activerecord-3.0.3/lib/active_record/associations/through_association_scope.rb	2010-12-15 19:27:34.000000000 -0200
@@ -53,7 +53,7 @@
       def construct_joins(custom_joins = nil)
         polymorphic_join = nil
         if @reflection.source_reflection.macro == :belongs_to
-          reflection_primary_key = @reflection.klass.primary_key
+          reflection_primary_key = @reflection.source_reflection.options[:primary_key] || @reflection.klass.primary_key
           source_primary_key     = @reflection.source_reflection.primary_key_name
           if @reflection.options[:source_type]
             polymorphic_join = "AND %s.%s = %s" % [