diff --git a/scripts/rollup/bundles.js b/scripts/rollup/bundles.js
index e5685f0115..c31c819917 100644
--- a/scripts/rollup/bundles.js
+++ b/scripts/rollup/bundles.js
@@ -369,6 +369,24 @@ const bundles = [
   },
 ];
 
+// Based on deep-freeze by substack (public domain)
+function deepFreeze(o) {
+  Object.freeze(o);
+  Object.getOwnPropertyNames(o).forEach(function(prop) {
+    if (
+      o[prop] !== null &&
+      (typeof o[prop] === 'object' || typeof o[prop] === 'function') &&
+      !Object.isFrozen(o[prop])
+    ) {
+      deepFreeze(o[prop]);
+    }
+  });
+  return o;
+}
+
+// Don't accidentally mutate config as part of the build
+deepFreeze(bundles);
+
 module.exports = {
   bundleTypes,
   bundles,
diff --git a/scripts/rollup/modules.js b/scripts/rollup/modules.js
index 3f7b4070cc..24c7d7a02c 100644
--- a/scripts/rollup/modules.js
+++ b/scripts/rollup/modules.js
@@ -143,7 +143,7 @@ function getExternalModules(externals, bundleType, isRenderer) {
   // this means having a require("name-of-external-module") at
   // the top of the bundle. for UMD bundles this means having
   // both a require and a global check for them
-  let externalModules = externals;
+  let externalModules = externals.slice();
 
   switch (bundleType) {
     case UMD_DEV:
@@ -158,7 +158,6 @@ function getExternalModules(externals, bundleType, isRenderer) {
     case RN_PROD:
       fbjsModules.forEach(module => externalModules.push(module));
       externalModules.push('object-assign');
-
       if (isRenderer) {
         externalModules.push('react');
       }
@@ -166,6 +165,7 @@ function getExternalModules(externals, bundleType, isRenderer) {
     case FB_DEV:
     case FB_PROD:
       fbjsModules.forEach(module => externalModules.push(module));
+      externalModules.push('object-assign');
       externalModules.push('ReactCurrentOwner');
       externalModules.push('lowPriorityWarning');
       if (isRenderer) {