diff --git a/src/iiiftilesource.js b/src/iiiftilesource.js
index 1105ea51..54ec073f 100644
--- a/src/iiiftilesource.js
+++ b/src/iiiftilesource.js
@@ -145,7 +145,7 @@ $.IIIFTileSource = function( options ){
     if( this.sizes ) {
         var sizeLength = this.sizes.length;
         if ( (sizeLength === options.maxLevel) || (sizeLength === options.maxLevel + 1) ) {
-            this.levelSizes = this.sizes;
+            this.levelSizes = this.sizes.slice().sort(( size1, size2 ) => size1.width - size2.width);
             // Need to take into account that the list may or may not include the full resolution size
             if( sizeLength === options.maxLevel ) {
                 this.levelSizes.push( {width: this.width, height: this.height} );
@@ -269,9 +269,6 @@ $.extend( $.IIIFTileSource.prototype, $.TileSource.prototype, /** @lends OpenSea
                     }
                 }
             }
-            data.sizes = data.sizes && data.sizes.sort(
-                ( size1, size2 ) => size1.width - size2.width
-            );
             return data;
         }
     },