diff --git a/chrome/content/zotero/xpcom/utilities.js b/chrome/content/zotero/xpcom/utilities.js
index a5622c66f8..e2f3cab5b6 100644
--- a/chrome/content/zotero/xpcom/utilities.js
+++ b/chrome/content/zotero/xpcom/utilities.js
@@ -277,7 +277,10 @@ Zotero.Utilities = {
 	 * Return isbn if valid, otherwise return false
 	 */
 	"cleanISBN":function(/**String*/ isbn) {
-		isbn = isbn.replace(/[^x\d]+/ig, '').toUpperCase();
+		isbn = isbn.replace(/[^0-9a-z]+/ig, '').toUpperCase()	//we only want to ignore punctuation, spaces
+						.match(/(?:97[89][0-9]{10}|[0-9]{9}[0-9X])/);	//13 digit or 10 digit
+		if(!isbn) return false;
+		isbn = isbn[0];
 
 		if(isbn.length == 10) {
 			// Verify ISBN-10 checksum
@@ -292,17 +295,11 @@ Zotero.Utilities = {
 			return (sum % 11 == 0) ? isbn : false;
 		}
 
-		isbn = isbn.replace(/X/g, '');	//get rid of Xs
-
 		if(isbn.length == 13) {
-			// ISBN-13 should start with 978 or 979 i.e. GS1 for book publishing industry
-			var prefix = isbn.slice(0,3);
-			if (prefix != "978" && prefix != "979") return false;
-
 			// Verify checksum
 			var sum = 0;
 			for (var i = 0; i < 12; i+=2) sum += isbn[i]*1;	//to make sure it's int
-			for (i = 1; i < 12; i+=2) sum += isbn[i]*3;
+			for (var i = 1; i < 12; i+=2) sum += isbn[i]*3;
 			sum += isbn[12]*1; //add the check digit
 
 			return (sum % 10 == 0 )? isbn : false;