diff --git a/src/ol/pointer/touchsource.js b/src/ol/pointer/touchsource.js
index f5e4ea4377..63d8ca68f2 100644
--- a/src/ol/pointer/touchsource.js
+++ b/src/ol/pointer/touchsource.js
@@ -31,6 +31,7 @@
 goog.provide('ol.pointer.TouchSource');
 
 goog.require('goog.array');
+goog.require('goog.asserts');
 goog.require('goog.math.Coordinate');
 goog.require('ol.pointer.EventSource');