diff --git a/spec/dummy/spec/requests/server_render_check_spec.rb b/spec/dummy/spec/requests/server_render_check_spec.rb
index b36aa3c47..f36bc45c1 100644
--- a/spec/dummy/spec/requests/server_render_check_spec.rb
+++ b/spec/dummy/spec/requests/server_render_check_spec.rb
@@ -63,6 +63,7 @@
       mail = DummyMailer.hello_email
       expect(mail.subject).to match "mail"
       expect(mail.body).to match "Mr. Mailing Server Side Rendering"
+      expect(mail.body).to match "inMailer":true"
     end
   end