diff --git a/boot/boot.js b/boot/boot.js
index 27b65694c..779237669 100644
--- a/boot/boot.js
+++ b/boot/boot.js
@@ -1854,7 +1854,8 @@ $tw.boot.startup = function(options) {
 	$tw.utils.registerFileType("audio/mp3","base64",".mp3");
 	$tw.utils.registerFileType("audio/mp4","base64",[".mp4",".m4a"]);
 	$tw.utils.registerFileType("text/x-markdown","utf8",[".md",".markdown"]);
-	$tw.utils.registerFileType("application/enex+xml","utf8",".enex");	
+	$tw.utils.registerFileType("application/enex+xml","utf8",".enex");
+	$tw.utils.registerFileType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet","base64",".xlsx");
 	// Create the wiki store for the app
 	$tw.wiki = new $tw.Wiki();
 	// Install built in tiddler fields modules