diff --git a/static/js/utils.js b/static/js/utils.js
index 3d7d1c6..fc7186f 100644
--- a/static/js/utils.js
+++ b/static/js/utils.js
@@ -1033,7 +1033,7 @@ oml.supportedExtensions = ['pdf', 'epub', 'kepub', 'cbr', 'cbz'];
 oml.upload = function(fileslist, callback) {
     var files = [], ids = [];
     for (var i = 0; i < fileslist.length; i++) {
-        var extension = Ox.last(fileslist[i].name.split('.'));
+        var extension = Ox.last(fileslist[i].name.split('.')).toLowerCase();
         if (Ox.contains(oml.supportedExtensions, extension)) {
             files.push(fileslist[i]);
         }