diff --git a/chrome/content/zotero/xpcom/utilities.js b/chrome/content/zotero/xpcom/utilities.js
index c5dba144d..eeaca7700 100644
--- a/chrome/content/zotero/xpcom/utilities.js
+++ b/chrome/content/zotero/xpcom/utilities.js
@@ -261,8 +261,9 @@ Zotero.Utilities = {
 		if(typeof(x) != "string") {
 			throw "cleanDOI: argument must be a string";
 		}
-		
-		return x.match(/10\.[0-9]{4,}\/[^\s]*[^\s\.,]/)[0];
+
+		var doi = x.match(/10\.[0-9]{4,}\/[^\s]*[^\s\.,]/);
+		return doi ? doi[0] : null;
 	},
 
 	/**