diff --git a/examples/vector-osm.js b/examples/vector-osm.js
index 8dd778508b..5834ef230e 100644
--- a/examples/vector-osm.js
+++ b/examples/vector-osm.js
@@ -95,7 +95,7 @@ var vectorSource = new ol.source.ServerVector({
     var url = 'http://overpass-api.de/api/xapi?map?bbox=' +
         epsg4326Extent.join(',');
     $.ajax(url).then(function(response) {
-      vectorSource.readFeatures(response);
+      vectorSource.addFeatures(vectorSource.readFeatures(response));
     });
   },
   strategy: ol.loadingstrategy.createTile(new ol.tilegrid.XYZ({
diff --git a/src/ol/source/formatvectorsource.js b/src/ol/source/formatvectorsource.js
index cb7d08dfb9..3b3ad39fd6 100644
--- a/src/ol/source/formatvectorsource.js
+++ b/src/ol/source/formatvectorsource.js
@@ -40,62 +40,18 @@ ol.source.FormatVector = function(options) {
    */
   this.format = options.format;
 
-  /**
-   * @protected
-   * @type {function(Event)}
-   */
-  this.handleXhrIo = goog.bind(this.handleXhrIo_, this);
-
 };
 goog.inherits(ol.source.FormatVector, ol.source.Vector);
 
 
-/**
- * @param {Event} event Event.
- * @private
- */
-ol.source.FormatVector.prototype.handleXhrIo_ = function(event) {
-  var xhrIo = event.target;
-  goog.asserts.assertInstanceof(xhrIo, goog.net.XhrIo);
-  if (xhrIo.isSuccess()) {
-    var type = this.format.getType();
-    /** @type {ArrayBuffer|Document|Node|Object|string|undefined} */
-    var source;
-    if (type == ol.format.FormatType.BINARY &&
-        ol.BrowserFeature.HAS_ARRAY_BUFFER) {
-      source = xhrIo.getResponse();
-      goog.asserts.assertInstanceof(source, ArrayBuffer);
-    } else if (type == ol.format.FormatType.JSON) {
-      source = xhrIo.getResponseText();
-    } else if (type == ol.format.FormatType.TEXT) {
-      source = xhrIo.getResponseText();
-    } else if (type == ol.format.FormatType.XML) {
-      if (!goog.userAgent.IE) {
-        source = xhrIo.getResponseXml();
-      }
-      if (!goog.isDefAndNotNull(source)) {
-        source = ol.xml.load(xhrIo.getResponseText());
-      }
-    } else {
-      goog.asserts.fail();
-    }
-    if (goog.isDefAndNotNull(source)) {
-      this.readFeatures(source);
-    } else {
-      this.setState(ol.source.State.ERROR);
-      goog.asserts.fail();
-    }
-  } else {
-    this.setState(ol.source.State.ERROR);
-  }
-  goog.dispose(xhrIo);
-};
-
-
 /**
  * @param {goog.Uri|string} url URL.
+ * @param {function(this: T, Array.<ol.Feature>)} callback Callback.
+ * @param {T} thisArg Value to use as `this` when executing `callback`.
+ * @template T
  */
-ol.source.FormatVector.prototype.loadFeaturesFromURL = function(url) {
+ol.source.FormatVector.prototype.loadFeaturesFromURL =
+    function(url, callback, thisArg) {
   var xhrIo = new goog.net.XhrIo();
   var type = this.format.getType();
   var responseType;
@@ -107,13 +63,55 @@ ol.source.FormatVector.prototype.loadFeaturesFromURL = function(url) {
     responseType = goog.net.XhrIo.ResponseType.TEXT;
   }
   xhrIo.setResponseType(responseType);
-  goog.events.listen(xhrIo, goog.net.EventType.COMPLETE, this.handleXhrIo);
+  goog.events.listen(xhrIo, goog.net.EventType.COMPLETE,
+      /**
+       * @param {Event} event Event.
+       * @private
+       * @this {ol.source.FormatVector}
+       */
+      function(event) {
+        var xhrIo = event.target;
+        goog.asserts.assertInstanceof(xhrIo, goog.net.XhrIo);
+        if (xhrIo.isSuccess()) {
+          var type = this.format.getType();
+          /** @type {ArrayBuffer|Document|Node|Object|string|undefined} */
+          var source;
+          if (type == ol.format.FormatType.BINARY &&
+              ol.BrowserFeature.HAS_ARRAY_BUFFER) {
+            source = xhrIo.getResponse();
+            goog.asserts.assertInstanceof(source, ArrayBuffer);
+          } else if (type == ol.format.FormatType.JSON) {
+            source = xhrIo.getResponseText();
+          } else if (type == ol.format.FormatType.TEXT) {
+            source = xhrIo.getResponseText();
+          } else if (type == ol.format.FormatType.XML) {
+            if (!goog.userAgent.IE) {
+              source = xhrIo.getResponseXml();
+            }
+            if (!goog.isDefAndNotNull(source)) {
+              source = ol.xml.load(xhrIo.getResponseText());
+            }
+          } else {
+            goog.asserts.fail();
+          }
+          if (goog.isDefAndNotNull(source)) {
+            callback.call(thisArg, this.readFeatures(source));
+          } else {
+            this.setState(ol.source.State.ERROR);
+            goog.asserts.fail();
+          }
+        } else {
+          this.setState(ol.source.State.ERROR);
+        }
+        goog.dispose(xhrIo);
+      }, false, this);
   xhrIo.send(url);
 };
 
 
 /**
  * @param {ArrayBuffer|Document|Node|Object|string} source Source.
+ * @return {Array.<ol.Feature>} Features.
  */
 ol.source.FormatVector.prototype.readFeatures = function(source) {
   var format = this.format;
@@ -133,6 +131,5 @@ ol.source.FormatVector.prototype.readFeatures = function(source) {
       }
     }
   }
-  this.addFeaturesInternal(features);
-  this.setState(ol.source.State.READY);
+  return features;
 };
diff --git a/src/ol/source/staticvectorsource.js b/src/ol/source/staticvectorsource.js
index e13de2eef4..6ebc8ad278 100644
--- a/src/ol/source/staticvectorsource.js
+++ b/src/ol/source/staticvectorsource.js
@@ -23,35 +23,51 @@ ol.source.StaticVector = function(options) {
   });
 
   if (goog.isDef(options.arrayBuffer)) {
-    this.readFeatures(options.arrayBuffer);
+    this.addFeaturesInternal(this.readFeatures(options.arrayBuffer));
   }
 
   if (goog.isDef(options.doc)) {
-    this.readFeatures(options.doc);
+    this.addFeaturesInternal(this.readFeatures(options.doc));
   }
 
   if (goog.isDef(options.node)) {
-    this.readFeatures(options.node);
+    this.addFeaturesInternal(this.readFeatures(options.node));
   }
 
   if (goog.isDef(options.object)) {
-    this.readFeatures(options.object);
+    this.addFeaturesInternal(this.readFeatures(options.object));
   }
 
   if (goog.isDef(options.text)) {
-    this.readFeatures(options.text);
+    this.addFeaturesInternal(this.readFeatures(options.text));
   }
 
   if (goog.isDef(options.url) || goog.isDef(options.urls)) {
     this.setState(ol.source.State.LOADING);
     if (goog.isDef(options.url)) {
-      this.loadFeaturesFromURL(options.url);
+      this.loadFeaturesFromURL(options.url,
+          /**
+           * @param {Array.<ol.Feature>} features Features.
+           * @this {ol.source.StaticVector}
+           */
+          function(features) {
+            this.addFeaturesInternal(features);
+            this.setState(ol.source.State.READY);
+          }, this);
     }
     if (goog.isDef(options.urls)) {
       var urls = options.urls;
       var i, ii;
       for (i = 0, ii = urls.length; i < ii; ++i) {
-        this.loadFeaturesFromURL(urls[i]);
+        this.loadFeaturesFromURL(urls[i],
+            /**
+             * @param {Array.<ol.Feature>} features Features.
+             * @this {ol.source.StaticVector}
+             */
+            function(features) {
+              this.addFeaturesInternal(features);
+              this.setState(ol.source.State.READY);
+            }, this);
       }
     }
   }