diff --git a/src/ol/interaction/dragrotateinteraction.js b/src/ol/interaction/dragrotateinteraction.js
index 681c86c654..60dfa35258 100644
--- a/src/ol/interaction/dragrotateinteraction.js
+++ b/src/ol/interaction/dragrotateinteraction.js
@@ -38,7 +38,7 @@ ol.interaction.DragRotate = function(opt_options) {
    * @private
    * @type {number|undefined}
    */
-  this.lastAngle_;
+  this.lastAngle_ = undefined;
 
 };
 goog.inherits(ol.interaction.DragRotate, ol.interaction.Drag);