2 files changed, 8 insertions, 9 deletions
diff --git a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
index 0ad5206980..34a555dfd4 100644
--- a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
+++ b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
@@ -15,7 +15,10 @@ module ActiveRecord::Associations::Builder
         end
 
         private
-        def klass; @rhs_class_name.constantize; end
+
+        def klass
+          @lhs_class.send(:compute_type, @rhs_class_name)
+        end
       end
 
       def self.build(lhs_class, name, options)
@@ -23,13 +26,7 @@ module ActiveRecord::Associations::Builder
           KnownTable.new options[:join_table].to_s
         else
           class_name = options.fetch(:class_name) {
-            model_name = name.to_s.camelize.singularize
-
-            if lhs_class.parent_name
-              model_name.prepend("#{lhs_class.parent_name}::")
-            end
-
-            model_name
+            name.to_s.camelize.singularize
           }
           KnownClass.new lhs_class, class_name
         end
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 175019a72b..35e176622d 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -93,7 +93,9 @@ module ActiveRecord
         end
 
         def through_scope_attributes
-          scope.where_values_hash(through_association.reflection.name.to_s).except!(through_association.reflection.foreign_key)
+          scope.where_values_hash(through_association.reflection.name.to_s).
+            except!(through_association.reflection.foreign_key,
+                    through_association.reflection.klass.inheritance_column)
         end
 
         def save_through_record(record)