diff --git a/app/assets/javascripts/discourse/components/avatar-uploader.js.es6 b/app/assets/javascripts/discourse/components/avatar-uploader.js.es6
index d5e983ccf8c..b4d4073c5d1 100644
--- a/app/assets/javascripts/discourse/components/avatar-uploader.js.es6
+++ b/app/assets/javascripts/discourse/components/avatar-uploader.js.es6
@@ -17,12 +17,12 @@ export default Em.Component.extend(UploadMixin, {
     // indeed, the server gives us back the url to the file we've just uploaded
     // often, this file is not a square, so we need to crop it properly
     // this will also capture the first frame of animated avatars when they're not allowed
-    Discourse.Utilities.cropAvatar(upload.url, upload.original_filename).then(avatarTemplate => {
+    Discourse.Utilities.cropAvatar(upload.url).then(avatarTemplate => {
       this.set("uploadedAvatarTemplate", avatarTemplate);
 
       // indicates the users is using an uploaded avatar (must happen after cropping, otherwise
       //  we will attempt to load an invalid avatar and cache a redirect to old one, uploadedAvatarTemplate
-      //  trumps over custom avatar upload id)
+      //  trumps over custom_avatar_upload_id)
       this.set("custom_avatar_upload_id", upload.id);
     });
 
diff --git a/app/assets/javascripts/discourse/controllers/edit-category.js.es6 b/app/assets/javascripts/discourse/controllers/edit-category.js.es6
index ca15eda2496..52e0e45bc2c 100644
--- a/app/assets/javascripts/discourse/controllers/edit-category.js.es6
+++ b/app/assets/javascripts/discourse/controllers/edit-category.js.es6
@@ -5,7 +5,6 @@ import { categoryBadgeHTML } from 'discourse/helpers/category-link';
 // Modal for editing / creating a category
 export default ObjectController.extend(ModalFunctionality, {
   foregroundColors: ['FFFFFF', '000000'],
-  categoryUploadUrl: '/uploads',
   editingPermissions: false,
   selectedTab: null,
   saving: false,
diff --git a/app/assets/javascripts/discourse/lib/utilities.js b/app/assets/javascripts/discourse/lib/utilities.js
index d85e474132e..76b24f5007f 100644
--- a/app/assets/javascripts/discourse/lib/utilities.js
+++ b/app/assets/javascripts/discourse/lib/utilities.js
@@ -310,11 +310,11 @@ Discourse.Utilities = {
 
     @method cropAvatar
     @param {String} url The url of the avatar
-    @param {String} fileType The file type of the uploaded file
     @returns {Promise} a promise that will eventually be the cropped avatar.
   **/
-  cropAvatar: function(url, fileType) {
-    if (Discourse.SiteSettings.allow_animated_avatars && fileType === "image/gif") {
+  cropAvatar: function(url) {
+    const extension = /\.(\w{2,})$/.exec(url)[1];
+    if (Discourse.SiteSettings.allow_animated_avatars && extension === "gif") {
       // can't crop animated gifs... let the browser stretch the gif
       return Ember.RSVP.resolve(url);
     } else {
@@ -344,7 +344,7 @@ Discourse.Utilities = {
           // draw the image into the canvas
           canvas.getContext("2d").drawImage(img, x, y, dimension, dimension, 0, 0, size, size);
           // retrieve the image from the canvas
-          resolve(canvas.toDataURL(fileType));
+          resolve(canvas.toDataURL("image/" + extension));
         };
         // launch the onload event
         image.src = url;
diff --git a/test/javascripts/lib/utilities-test.js.es6 b/test/javascripts/lib/utilities-test.js.es6
index 75d4f14b869..47088b30351 100644
--- a/test/javascripts/lib/utilities-test.js.es6
+++ b/test/javascripts/lib/utilities-test.js.es6
@@ -177,7 +177,7 @@ module("Discourse.Utilities.cropAvatar with animated avatars", {
 asyncTestDiscourse("cropAvatar", function() {
   expect(1);
 
-  utils.cropAvatar("/path/to/avatar.gif", "image/gif").then(function(avatarTemplate) {
+  utils.cropAvatar("/path/to/avatar.gif").then(function(avatarTemplate) {
     equal(avatarTemplate, "/path/to/avatar.gif", "returns the url to the gif when animated gif are enabled");
     start();
   });