diff --git a/package.json b/package.json
index 3935c174..a4f4c082 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,8 @@
   "scripts": {
     "test": "node_modules/.bin/impunity --entry-point src/main.js --force-esm",
     "start": "node scripts/serve-local.js",
-    "build": "node --experimental-modules scripts/build.mjs"
+    "build": "node --experimental-modules scripts/build.mjs",
+    "postinstall": "node ./scripts/post-install.mjs"
   },
   "repository": {
     "type": "git",
@@ -46,6 +47,7 @@
     "xxhash": "^0.3.0"
   },
   "dependencies": {
+    "another-json": "^0.2.0",
     "olm": "https://packages.matrix.org/npm/olm/olm-3.1.4.tgz"
   }
 }
diff --git a/scripts/post-install.mjs b/scripts/post-install.mjs
new file mode 100644
index 00000000..3b287fd9
--- /dev/null
+++ b/scripts/post-install.mjs
@@ -0,0 +1,53 @@
+/*
+Copyright 2020 Bruno Windels <bruno@windels.cloud>
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import fsRoot from "fs";
+const fs = fsRoot.promises;
+import path from "path";
+import { rollup } from 'rollup';
+import { fileURLToPath } from 'url';
+import { dirname } from 'path';
+// needed to translate commonjs modules to esm
+import commonjs from '@rollup/plugin-commonjs';
+// multi-entry plugin so we can add polyfill file to main
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+const projectDir = path.join(__dirname, "../");
+
+async function commonjsToESM(src, dst) {
+    // create js bundle
+    const bundle = await rollup({
+        input: src,
+        plugins: [commonjs()]
+    });
+    const {output} = await bundle.generate({
+        format: 'es'
+    });
+    const code = output[0].code;
+    await fs.writeFile(dst, code, "utf8");
+}
+
+async function transpile() {
+    await fs.mkdir(path.join(projectDir, "lib/another-json/"));
+    await commonjsToESM(
+        path.join(projectDir, 'node_modules/another-json/another-json.js'),
+        path.join(projectDir, "lib/another-json/index.js")
+    );
+}
+
+transpile();
diff --git a/yarn.lock b/yarn.lock
index 9e556624..ea3c6ba5 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -907,6 +907,11 @@
   dependencies:
     "@types/node" "*"
 
+another-json@^0.2.0:
+  version "0.2.0"
+  resolved "https://registry.yarnpkg.com/another-json/-/another-json-0.2.0.tgz#b5f4019c973b6dd5c6506a2d93469cb6d32aeedc"
+  integrity sha1-tfQBnJc7bdXGUGotk0acttMq7tw=
+
 ansi-styles@^3.2.1:
   version "3.2.1"
   resolved "https://registry.yarnpkg.com/ansi-styles/-/ansi-styles-3.2.1.tgz#41fbb20243e50b12be0f04b8dedbf07520ce841d"