diff --git a/test/tests/pdfReaderTest.js b/test/tests/pdfReaderTest.js
index 3dc96a6df0..6b7ac8f982 100644
--- a/test/tests/pdfReaderTest.js
+++ b/test/tests/pdfReaderTest.js
@@ -18,7 +18,7 @@ describe("PDF Reader", function () {
 			var reader = await Zotero.Reader.open(attachment.itemID);
 			// TODO: Implement a promise that would be resolved when pdf-reader is completely loaded
 			var n = 0;
-			while (!reader._iframeWindow.wrappedJSObject.PDFViewerApplication.pdfDocument && n++ < 50) {
+			while ((!reader._iframeWindow || !reader._iframeWindow.wrappedJSObject.PDFViewerApplication.pdfDocument) && n++ < 50) {
 				await Zotero.Promise.delay(100);
 			}
 			await reader._iframeWindow.wrappedJSObject.viewerInstance._viewer._pdfjsPromise;