diff --git a/chrome/content/zotero/xpcom/translation/translate.js b/chrome/content/zotero/xpcom/translation/translate.js
index 5b588936b3..66a38c3603 100644
--- a/chrome/content/zotero/xpcom/translation/translate.js
+++ b/chrome/content/zotero/xpcom/translation/translate.js
@@ -616,6 +616,32 @@ Zotero.Translate.Sandbox = {
 					if(setShortTitle) item.shortTitle = title;
 				}
 				
+				/* Clean up ISBNs
+				 * Allow multiple ISBNs, but...
+				 * (1) validate all ISBNs
+				 * (2) convert all ISBNs to ISBN-13
+				 * (3) remove any duplicates
+				 * (4) separate them with space
+				 */
+				if (item.ISBN) {
+					// Match ISBNs with groups separated by various dashes or even spaces
+					var isbnRe = /\b(?:97[89][\s\x2D\xAD\u2010-\u2015\u2043\u2212]*)?(?:\d[\s\x2D\xAD\u2010-\u2015\u2043\u2212]*){9}[\dx](?![\x2D\xAD\u2010-\u2015\u2043\u2212])\b/gi,
+						validISBNs = [],
+						isbn;
+					while (isbn = isbnRe.exec(item.ISBN)) {
+						var validISBN = Zotero.Utilities.cleanISBN(isbn[0]);
+						if (!validISBN) {
+							// Back up and move up one character
+							isbnRe.lastIndex = isbn.index + 1;
+							continue;
+						}
+						
+						var isbn13 = Zotero.Utilities.toISBN13(validISBN);
+						if (validISBNs.indexOf(isbn13) == -1) validISBNs.push(isbn13);
+					}
+					item.ISBN = validISBNs.join(' ');
+				}
+				
 				// refuse to save very long tags
 				if(item.tags) {
 					for(var i=0; i<item.tags.length; i++) {
diff --git a/chrome/content/zotero/xpcom/utilities.js b/chrome/content/zotero/xpcom/utilities.js
index 3e62855fe0..a81a11dabd 100644
--- a/chrome/content/zotero/xpcom/utilities.js
+++ b/chrome/content/zotero/xpcom/utilities.js
@@ -310,6 +310,34 @@ Zotero.Utilities = {
 
 		return false;
 	},
+	
+	/*
+	 * Convert ISBN 10 to ISBN 13
+	 * @param {String} isbn ISBN 10 or ISBN 13
+	 *   cleanISBN
+	 * @return {String} ISBN-13
+	 */
+	"toISBN13": function(isbn) {
+		if (!/^(?:97[89])?\d{9}[\dxX]$/.test(isbn)
+			&& !(isbn = Zotero.Utilities.cleanISBN(isbn))
+		) {
+			throw new Error('Invalid ISBN: ' + isbn);
+		}
+		
+		if (isbn.length == 13) return isbn; // Recalculate check digit?
+		
+		isbn = '978' + isbn.substr(0,9);
+		
+		var sum = 0;
+		for (var i = 0; i < 12; i++) {
+			sum += isbn[i] * (i%2 ? 3 : 1);
+		}
+		
+		var checkDigit = 10 - (sum % 10);
+		if (checkDigit == 10) checkDigit = 0;
+		
+		return isbn + checkDigit;
+	},
 
 	/**
 	 * Clean and validate ISSN.