diff --git a/src/ol/interaction/pointer.js b/src/ol/interaction/pointer.js
index 6632a7f555..e288738370 100644
--- a/src/ol/interaction/pointer.js
+++ b/src/ol/interaction/pointer.js
@@ -69,7 +69,7 @@ ol.interaction.Pointer = function(opt_options) {
   this.handlingDownUpSequence = false;
 
   /**
-   * @type {Object.<number, ol.pointer.PointerEvent>}
+   * @type {Object.<string, ol.pointer.PointerEvent>}
    * @private
    */
   this.trackedPointers_ = {};
@@ -123,14 +123,15 @@ ol.interaction.Pointer.prototype.updateTrackedPointers_ = function(mapBrowserEve
   if (this.isPointerDraggingEvent_(mapBrowserEvent)) {
     var event = mapBrowserEvent.pointerEvent;
 
+    var id = event.pointerId.toString();
     if (mapBrowserEvent.type == ol.MapBrowserEventType.POINTERUP) {
-      delete this.trackedPointers_[event.pointerId];
+      delete this.trackedPointers_[id];
     } else if (mapBrowserEvent.type ==
         ol.MapBrowserEventType.POINTERDOWN) {
-      this.trackedPointers_[event.pointerId] = event;
-    } else if (event.pointerId in this.trackedPointers_) {
+      this.trackedPointers_[id] = event;
+    } else if (id in this.trackedPointers_) {
       // update only when there was a pointerdown event for this pointer
-      this.trackedPointers_[event.pointerId] = event;
+      this.trackedPointers_[id] = event;
     }
     this.targetPointers = ol.obj.getValues(this.trackedPointers_);
   }