1 files changed, 7 insertions, 1 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 e472277374..a297439214 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
@@ -23,7 +23,13 @@ module ActiveRecord::Associations::Builder
           KnownTable.new options[:join_table].to_s
         else
           class_name = options.fetch(:class_name) {
-            name.to_s.camelize.singularize
+            model_name = name.to_s.camelize.singularize
+
+            if parent_name = lhs_class.parent_name
+              model_name = model_name.prepend("#{parent_name}::")
+            end
+
+            model_name
           }
           KnownClass.new lhs_class, class_name
         end