diff --git a/chrome/content/zotero/xpcom/utilities.js b/chrome/content/zotero/xpcom/utilities.js
index 318bd78b1e..945a40ee6b 100644
--- a/chrome/content/zotero/xpcom/utilities.js
+++ b/chrome/content/zotero/xpcom/utilities.js
@@ -1346,7 +1346,7 @@ Zotero.Utilities = {
 		//Special handling for Error or Exception
 		var isException = Zotero.isFx && !Zotero.isBookmarklet && obj instanceof Components.interfaces.nsIException;
 		var isError = obj instanceof Error;
-		if (!isException && !isError && obj.constructor && obj.stack) {
+		if (!isException && !isError && constructor in obj && stack in obj) {
 			switch (obj.constructor.name) {
 				case 'Error':
 				case 'EvalError':