diff --git a/examples/wms-custom-proj.js b/examples/wms-custom-proj.js
index fea7b563dd..20b2b90072 100644
--- a/examples/wms-custom-proj.js
+++ b/examples/wms-custom-proj.js
@@ -29,9 +29,8 @@ ol.Projection.addProjection(epsg21781);
 // We give the single image source a set of resolutions. This prevents the
 // source from requesting images of arbitrary resolutions.
 var projectionExtent = epsg21781.getExtent();
-var maxResolution = Math.max(
-    projectionExtent.maxX - projectionExtent.minX,
-    projectionExtent.maxY - projectionExtent.minY) / 256;
+var maxResolution = Math.max(projectionExtent.getWidth(),
+    projectionExtent.getHeight()) / 256;
 var resolutions = new Array(10);
 for (var i = 0; i < 10; ++i) {
   resolutions[i] = maxResolution / Math.pow(2.0, i);
diff --git a/src/ol/extent.exports b/src/ol/extent.exports
index 23e1785d4f..b52ee8007a 100644
--- a/src/ol/extent.exports
+++ b/src/ol/extent.exports
@@ -1,2 +1,3 @@
 @exportSymbol ol.Extent
-
+@exportProperty ol.Extent.prototype.getHeight
+@exportProperty ol.Extent.prototype.getWidth
diff --git a/src/imageurlfunction.js b/src/ol/imageurlfunction.js
similarity index 96%
rename from src/imageurlfunction.js
rename to src/ol/imageurlfunction.js
index bb328819eb..ebaec5c427 100644
--- a/src/imageurlfunction.js
+++ b/src/ol/imageurlfunction.js
@@ -1,6 +1,7 @@
 goog.provide('ol.ImageUrlFunction');
 goog.provide('ol.ImageUrlFunctionType');
 
+goog.require('goog.uri.utils');
 goog.require('ol.Extent');
 goog.require('ol.Size');
 
diff --git a/src/ol/source/singleimagewmssource.js b/src/ol/source/singleimagewmssource.js
index 3529678443..84e66db61f 100644
--- a/src/ol/source/singleimagewmssource.js
+++ b/src/ol/source/singleimagewmssource.js
@@ -1,5 +1,6 @@
 goog.provide('ol.source.SingleImageWMS');
 
+goog.require('goog.uri.utils');
 goog.require('ol.Extent');
 goog.require('ol.Image');
 goog.require('ol.ImageUrlFunction');