diff --git a/package.json b/package.json
index a03123bea8..5a399d386e 100644
--- a/package.json
+++ b/package.json
@@ -45,7 +45,7 @@
     "pbf": "3.0.5",
     "pixelworks": "1.1.0",
     "rbush": "2.0.1",
-    "rollup": "^0.42.0",
+    "rollup": "^0.45.0",
     "rollup-plugin-cleanup": "^1.0.0",
     "rollup-plugin-commonjs": "^8.0.2",
     "rollup-plugin-node-resolve": "^3.0.0",
diff --git a/tasks/build-ext.js b/tasks/build-ext.js
index 211e5df494..18651389c5 100644
--- a/tasks/build-ext.js
+++ b/tasks/build-ext.js
@@ -47,6 +47,7 @@ function main() {
   return Promise.all(pkg.ext.map(ext => {
     const moduleName = ext.name || ext.module;
     const options = {
+      extend: true,
       entry: require.resolve(ext.module),
       dest: `${path.join(__dirname, '..', 'build', 'ol.ext', moduleName.toLowerCase())}.js`,
       format: 'iife',