diff --git a/test/content/runtests.js b/test/content/runtests.js
index e2398f15c..2d29ad4aa 100644
--- a/test/content/runtests.js
+++ b/test/content/runtests.js
@@ -212,6 +212,7 @@ if(run && ZoteroUnit.tests) {
 		var el = document.createElement("script");
 		el.type = "application/javascript;version=1.8";
 		el.src = "resource://zotero-unit-tests/"+fname;
+		el.async = false;
 		document.body.appendChild(el);
 	}
 }