diff --git a/lib/active_admin/form_builder.rb b/lib/active_admin/form_builder.rb
index 009e9d8e110..48c4676073b 100644
--- a/lib/active_admin/form_builder.rb
+++ b/lib/active_admin/form_builder.rb
@@ -95,7 +95,7 @@ def content_has_many(&block)
       contents = without_wrapper { inputs(options, &form_block) }
       contents ||= "".html_safe
 
-      js = new_record ? js_for_has_many(options[:class], &form_block) : ""
+      js = new_record ? js_for_has_many(&form_block) : ""
       contents << js
     end
 
@@ -159,14 +159,13 @@ def without_wrapper
     end
 
     # Capture the ADD JS
-    def js_for_has_many(class_string, &form_block)
+    def js_for_has_many(&form_block)
       assoc_name = assoc_klass.model_name
-      placeholder = "NEW_#{assoc_name.to_s.underscore.upcase.gsub(/\//, '_')}_RECORD"
-      opts = {
+      placeholder = "NEW_#{assoc_name.to_s.underscore.upcase.tr('/', '_')}_RECORD"
+      opts = options.merge(
         for: [assoc, assoc_klass.new],
-        class: class_string,
         for_options: { child_index: placeholder }
-      }
+      )
       html = template.capture { __getobj__.send(:inputs_for_nested_attributes, opts, &form_block) }
       text = new_record.is_a?(String) ? new_record : I18n.t("active_admin.has_many_new", model: assoc_name.human)
 
diff --git a/spec/unit/form_builder_spec.rb b/spec/unit/form_builder_spec.rb
index eba404e7685..4260af49ea2 100644
--- a/spec/unit/form_builder_spec.rb
+++ b/spec/unit/form_builder_spec.rb
@@ -648,6 +648,48 @@ def user
       end
     end
 
+    describe "with custom class" do
+      let :body do
+        build_form({ url: "/categories" }, Category.new) do |f|
+          f.object.posts.build
+          f.has_many :posts, class: 'myclass' do |p|
+            p.input :title
+          end
+        end
+      end
+
+      it "should generate a fieldset with the given class" do
+        expect(body).to have_css(".has_many_container > fieldset.myclass")
+      end
+
+      it "should add the custom class on the fieldset generated by the new record link" do
+        link = body.find(".has_many_container > a.has_many_add")
+        new_record_html = Capybara.string(link[:'data-html'])
+        expect(new_record_html).to have_css("fieldset.myclass")
+      end
+    end
+
+    describe "with custom attributes" do
+      let :body do
+        build_form({ url: "/categories" }, Category.new) do |f|
+          f.object.posts.build
+          f.has_many :posts, attr: "value", data: { 'custom-attribute': "custom-value" } do |p|
+            p.input :title
+          end
+        end
+      end
+
+      it "should generate a fieldset with the given custom attributes" do
+        expect(body).to have_css(".has_many_container > fieldset[attr='value'][data-custom-attribute='custom-value']")
+      end
+
+      it "should add custom attributes on the fieldset generated by the new record link" do
+        link = body.find(".has_many_container > a.has_many_add")
+        new_record_html = Capybara.string(link[:'data-html'])
+        expect(new_record_html).to have_css("fieldset[attr='value'][data-custom-attribute='custom-value']")
+      end
+    end
+
     describe "with allow destroy" do
       shared_examples_for "has many with allow_destroy = true" do |child_num|
         it "should render the nested form" do