diff --git a/src/ol/extent.js b/src/ol/extent.js
index 5a28036f51..cf393fd61b 100644
--- a/src/ol/extent.js
+++ b/src/ol/extent.js
@@ -201,6 +201,19 @@ ol.extent.extendCoordinate = function(extent, coordinate) {
 };
 
 
+/**
+ * @param {ol.Extent} extent Extent.
+ * @param {number} x X.
+ * @param {number} y Y.
+ */
+ol.extent.extendXY = function(extent, x, y) {
+  extent[0] = Math.min(extent[0], x);
+  extent[1] = Math.min(extent[1], y);
+  extent[2] = Math.max(extent[2], x);
+  extent[3] = Math.max(extent[3], y);
+};
+
+
 /**
  * @param {ol.Extent} extent Extent.
  * @return {ol.Coordinate} Bottom left coordinate.