diff --git a/src/export.js b/src/export.js
index e0bd6da3b..9d5d0415f 100644
--- a/src/export.js
+++ b/src/export.js
@@ -1,18 +1,39 @@
 /* global module, exports, define */
 import { window, document, globalThis } from './globals';
 
+/**
+ * Available exports:
+ *
+ * globalThis:
+ * - browser (globalThis === window)
+ * - Web Worker (globalThis === self)
+ * - Node.js
+ * - SpiderMonkey (mozjs)
+ * - Rhino (since 7.14)
+ * - any other embedded JS engine
+ *
+ * CommonJS module.exports (commonjs2):
+ * - Node.js
+ *
+ * CommonJS exports (commonjs, https://wiki.commonjs.org/wiki/Modules):
+ * - Rhino
+ *
+ * AMD (RequireJS):
+ *  - Browser
+ */
 export default function exportQUnit (QUnit) {
-  let exportedModule = false;
-
-  if (window && document) {
-    // QUnit may be defined when it is preconfigured but then only QUnit and QUnit.config may be defined.
-    if (window.QUnit && window.QUnit.version) {
-      throw new Error('QUnit has already been defined.');
-    }
-
-    window.QUnit = QUnit;
-
-    exportedModule = true;
+  // If there is a placeholder QUnit global for preconfiguration,
+  // we must replace it with the real one. Such placeholder can be recognised
+  // by not having QUnit.version (it should only contain a QUnit.config property).
+  //
+  // If a real QUnit global is already defined, then replace our reference with that one.
+  // Since QUnit 3.0, we no longer throw an error if QUnit is loaded twice.
+  // This enables supporting mixed use of ESM import and CJS require() in a project,
+  // in a way that avoids split-brain problems for QUnit state.
+  if (globalThis.QUnit && globalThis.QUnit.version) {
+    QUnit = globalThis.QUnit;
+  } else {
+    globalThis.QUnit = QUnit;
   }
 
   // For Node.js
@@ -21,15 +42,11 @@ export default function exportQUnit (QUnit) {
 
     // For consistency with CommonJS environments' exports
     module.exports.QUnit = QUnit;
-
-    exportedModule = true;
   }
 
   // For CommonJS with exports, but without module.exports, like Rhino
   if (typeof exports !== 'undefined' && exports) {
     exports.QUnit = QUnit;
-
-    exportedModule = true;
   }
 
   // For AMD
@@ -38,13 +55,5 @@ export default function exportQUnit (QUnit) {
       return QUnit;
     });
     QUnit.config.autostart = false;
-
-    exportedModule = true;
-  }
-
-  // For other environments, including Web Workers (globalThis === self),
-  // SpiderMonkey (mozjs), and other embedded JavaScript engines
-  if (!exportedModule) {
-    globalThis.QUnit = QUnit;
   }
 }