diff --git a/src/ol/control/scalelinecontrol.js b/src/ol/control/scalelinecontrol.js
index 4f43d8ce3d..37f779a2f0 100644
--- a/src/ol/control/scalelinecontrol.js
+++ b/src/ol/control/scalelinecontrol.js
@@ -77,7 +77,7 @@ ol.control.ScaleLine = function(opt_options) {
    * @private
    * @type {number|undefined}
    */
-  this.renderedWidth_;
+  this.renderedWidth_ = undefined;
 
   /**
    * @private
diff --git a/src/ol/control/zoomslidercontrol.js b/src/ol/control/zoomslidercontrol.js
index 5fb6a454ea..5af6be81e6 100644
--- a/src/ol/control/zoomslidercontrol.js
+++ b/src/ol/control/zoomslidercontrol.js
@@ -38,10 +38,10 @@ ol.control.ZoomSlider = function(options) {
   /**
    * Will hold the current resolution of the view.
    *
-   * @type {number}
+   * @type {number|undefined}
    * @private
    */
-  this.currentResolution_;
+  this.currentResolution_ = undefined;
 
   /**
    * The direction of the slider. Will be determined from actual display of the