diff --git a/lib/tasks/themes.rake b/lib/tasks/themes.rake
index 83c1038a855..f11a628bec5 100644
--- a/lib/tasks/themes.rake
+++ b/lib/tasks/themes.rake
@@ -114,6 +114,7 @@ task "themes:qunit", :type, :value do |t, args|
     MSG
   end
   ENV["THEME_#{type.upcase}"] = value.to_s
+  ENV["QUNIT_RAILS_ENV"] ||= 'development' # qunit:test will switch to `test` by default
   Rake::Task["qunit:test"].reenable
   Rake::Task["qunit:test"].invoke(1200000, "/theme-qunit")
 end