diff --git a/addon/src/index.js b/addon/src/index.js
index 045c482c..8c3660b5 100644
--- a/addon/src/index.js
+++ b/addon/src/index.js
@@ -1,13 +1,30 @@
 /* globals Testem */
-import 'qunit/qunit/qunit.css';
-
 import { macroCondition, getOwnConfig, importSync } from '@embroider/macros';
 
+/**
+ * Load qunit-theme-ember by default, if no custom theme is specified.
+ */
+if (
+  macroCondition(
+    getOwnConfig()?.theme === undefined ||
+      getOwnConfig()?.theme === 'qunit-default' ||
+      getOwnConfig()?.theme === 'ember'
+  )
+) {
+  importSync('qunit/qunit/qunit.css');
+}
+
 if (macroCondition(!getOwnConfig()?.disableContainerStyles)) {
   importSync('./test-container-styles.css');
 }
 
-importSync('qunit-theme-ember/qunit.css');
+if (
+  macroCondition(
+    getOwnConfig()?.theme === undefined || getOwnConfig()?.theme === 'ember'
+  )
+) {
+  importSync('qunit-theme-ember/qunit.css');
+}
 
 export { default as QUnitAdapter, nonTestDoneCallback } from './adapter';
 export { loadTests } from './test-loader';