diff --git a/src/ol/geom/linestring.js b/src/ol/geom/linestring.js
index f89bc1a46a..7305604068 100644
--- a/src/ol/geom/linestring.js
+++ b/src/ol/geom/linestring.js
@@ -148,7 +148,7 @@ ol.geom.LineString.prototype.getCoordinateAtM = function(m, opt_extrapolate) {
       this.layout != ol.geom.GeometryLayout.XYZM) {
     return null;
   }
-  var extrapolate = goog.isDef(opt_extrapolate) ? opt_extrapolate : false;
+  var extrapolate = opt_extrapolate ? opt_extrapolate : false;
   return ol.geom.flat.lineStringCoordinateAtM(this.flatCoordinates, 0,
       this.flatCoordinates.length, this.stride, m, extrapolate);
 };