diff --git a/sources/osgPlugins/ReaderWriterZIP.js b/sources/osgPlugins/ReaderWriterZIP.js
index eb9405b94..30313f071 100644
--- a/sources/osgPlugins/ReaderWriterZIP.js
+++ b/sources/osgPlugins/ReaderWriterZIP.js
@@ -22,9 +22,9 @@ ReaderWriterZIP.prototype = {
         var self = this;
         if (options && options.filesMap !== undefined) {
             // it comes  from drag'n drop
-            if (options.filesMap[url] !== undefined) {
+            if (options.filesMap.has(url) !== undefined) {
                 // Now url is a File
-                var file = options.filesMap[url];
+                var file = options.filesMap.get(url);
                 return this.readZipFile(file).then(function() {
                     if (!self._fileName) return P.reject(self);
                     // At this point we have the main file name and a Map containing all the resources
@@ -40,7 +40,7 @@ ReaderWriterZIP.prototype = {
         });
 
         return filePromise.then(function(zfile) {
-            self.readZipFile(zfile).then(function() {
+            return self.readZipFile(zfile).then(function() {
                 // At this point we have the main file name and a Map containing all the resources
                 return ReaderParser.readNodeURL(self._fileName, {
                     filesMap: self._filesMap
@@ -50,7 +50,7 @@ ReaderWriterZIP.prototype = {
     },
 
     readZipFile: function(fileOrBlob) {
-        fileHelper.unzip(fileOrBlob).then(
+        return fileHelper.unzip(fileOrBlob).then(
             function(filesMap) {
                 for (var fileName in filesMap) {
                     var extension = fileHelper.getExtension(fileName);
@@ -64,6 +64,7 @@ ReaderWriterZIP.prototype = {
                         break;
                     }
                 }
+                this._filesMap = filesMap;
             }.bind(this)
         );
     }