diff --git a/package.json b/package.json
index d28e2bb..db638b8 100644
--- a/package.json
+++ b/package.json
@@ -4,6 +4,7 @@
   "private": true,
   "dependencies": {
     "ical.js": "^1.2.2",
+    "immutable": "^4.0.0-rc.9",
     "isomorphic-fetch": "^2.1.1",
     "localforage": "^1.5.5",
     "material-ui": "^0.20.0",
diff --git a/tsconfig.json b/tsconfig.json
index 8597354..cd129d8 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -2,7 +2,7 @@
   "compilerOptions": {
     "outDir": "build/dist",
     "module": "esnext",
-    "target": "es5",
+    "target": "es2015",
     "lib": ["es6", "dom"],
     "sourceMap": true,
     "allowJs": true,
diff --git a/yarn.lock b/yarn.lock
index 745d4b4..e7ba3b1 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2529,6 +2529,10 @@ immediate@~3.0.5:
   version "3.0.6"
   resolved "https://registry.yarnpkg.com/immediate/-/immediate-3.0.6.tgz#9db1dbd0faf8de6fbe0f5dd5e56bb606280de69b"
 
+immutable@^4.0.0-rc.9:
+  version "4.0.0-rc.9"
+  resolved "https://registry.yarnpkg.com/immutable/-/immutable-4.0.0-rc.9.tgz#1e6e0094e649013ec3742d2b5aeeca5eeda4f0bf"
+
 imurmurhash@^0.1.4:
   version "0.1.4"
   resolved "https://registry.yarnpkg.com/imurmurhash/-/imurmurhash-0.1.4.tgz#9218b9b2b928a238b13dc4fb6b6d576f231453ea"