diff --git a/packages/metro/src/DeltaBundler/DeltaTransformer.js b/packages/metro/src/DeltaBundler/DeltaTransformer.js
index 20a4ae4d..020a6527 100644
--- a/packages/metro/src/DeltaBundler/DeltaTransformer.js
+++ b/packages/metro/src/DeltaBundler/DeltaTransformer.js
@@ -17,6 +17,7 @@ const DeltaCalculator = require('./DeltaCalculator');
 const addParamsToDefineCall = require('../lib/addParamsToDefineCall');
 const createModuleIdFactory = require('../lib/createModuleIdFactory');
 const defaults = require('../defaults');
+const getPreludeCode = require('../lib/getPreludeCode');
 const nullthrows = require('fbjs/lib/nullthrows');
 const path = require('path');
 const removeInlineRequiresBlacklistFromOptions = require('../lib/removeInlineRequiresBlacklistFromOptions');
@@ -324,6 +325,8 @@ class DeltaTransformer extends EventEmitter {
     transformOptions: JSTransformerOptions,
     dependencyEdges: DependencyEdges,
   ): Promise<DeltaEntries> {
+    const preludeId = this._getModuleId('__prelude__');
+
     // Get all the polyfills from the relevant option params (the
     // `getPolyfills()` method and the `polyfillModuleNames` variable).
     const polyfillModuleNames = this._getPolyfills({
@@ -332,7 +335,7 @@ class DeltaTransformer extends EventEmitter {
 
     // Build the module system dependencies (scripts that need to
     // be included at the very beginning of the bundle) + any polifyll.
-    const modules = this._getModuleSystemDependencies()
+    const modules = [defaults.moduleSystem]
       .concat(polyfillModuleNames)
       .map(polyfillModuleName =>
         this._dependencyGraph.createPolyfill({
@@ -342,11 +345,23 @@ class DeltaTransformer extends EventEmitter {
         }),
       );
 
-    return await this._transformModules(
+    const transformedModules = await this._transformModules(
       modules,
       transformOptions,
       dependencyEdges,
     );
+    // The prelude needs to be the first thing in the file, and the insertion
+    // order of entries in the Map is significant.
+    return new Map([
+      [preludeId, this._getPrelude(preludeId)],
+      ...transformedModules,
+    ]);
+  }
+
+  _getPrelude(id: number): DeltaEntry {
+    const code = getPreludeCode({isDev: this._bundleOptions.dev});
+    const name = '__prelude__';
+    return {code, id, map: [], name, source: code, path: name, type: 'script'};
   }
 
   async _getAppend(dependencyEdges: DependencyEdges): Promise<DeltaEntries> {
@@ -526,16 +541,6 @@ class DeltaTransformer extends EventEmitter {
   _onFileChange = () => {
     this.emit('change');
   };
-
-  _getModuleSystemDependencies() {
-    const prelude = this._bundleOptions.dev
-      ? path.resolve(__dirname, '../lib/polyfills/prelude_dev.js')
-      : path.resolve(__dirname, '../lib/polyfills/prelude.js');
-
-    const moduleSystem = defaults.moduleSystem;
-
-    return [prelude, moduleSystem];
-  }
 }
 
 module.exports = DeltaTransformer;
diff --git a/packages/metro/src/ModuleGraph/ModuleGraph.js b/packages/metro/src/ModuleGraph/ModuleGraph.js
index d0d49af2..1eea315b 100644
--- a/packages/metro/src/ModuleGraph/ModuleGraph.js
+++ b/packages/metro/src/ModuleGraph/ModuleGraph.js
@@ -13,6 +13,7 @@
 
 const defaults = require('../defaults');
 const virtualModule = require('./module').virtual;
+const getPreludeCode = require('../lib/getPreludeCode');
 
 import type {BuildResult, GraphFn, PostProcessModules} from './types.flow';
 
@@ -54,7 +55,7 @@ exports.createBuildSetup = (
   ]);
 
   const {entryModules} = graph;
-  const preludeScript = prelude(optimize);
+  const preludeScript = virtualModule(getPreludeCode({isDev: !optimize}));
   const prependedScripts = [preludeScript, ...moduleSystem, ...polyfills];
   return {
     entryModules,
@@ -62,11 +63,3 @@ exports.createBuildSetup = (
     prependedScripts,
   };
 };
-
-function prelude(optimize) {
-  return virtualModule(
-    `var __DEV__=${String(!optimize)},` +
-      '__BUNDLE_START_TIME__=this.nativePerformanceNow?nativePerformanceNow():Date.now(),' +
-      `process={env:{NODE_ENV:'${optimize ? 'production' : 'development'}'}};`,
-  );
-}
diff --git a/packages/metro/src/integration_tests/__tests__/__snapshots__/basic_bundle-test.js.snap b/packages/metro/src/integration_tests/__tests__/__snapshots__/basic_bundle-test.js.snap
index 46d79572..40681153 100644
--- a/packages/metro/src/integration_tests/__tests__/__snapshots__/basic_bundle-test.js.snap
+++ b/packages/metro/src/integration_tests/__tests__/__snapshots__/basic_bundle-test.js.snap
@@ -1,15 +1,7 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`basic_bundle bundles package with polyfills 1`] = `
-"(function (global) {
-  global.__DEV__ = false;
-  global.__BUNDLE_START_TIME__ = global.nativePerformanceNow ? global.nativePerformanceNow() : Date.now();
-  global.process = {
-    env: {
-      NODE_ENV: 'production'
-    }
-  };
-})(this);
+"var __DEV__=false,__BUNDLE_START_TIME__=this.nativePerformanceNow?nativePerformanceNow():Date.now(),process={env:{NODE_ENV:'production'}};
 (function (global) {
   'use strict';
 
@@ -197,15 +189,7 @@ require(4);"
 `;
 
 exports[`basic_bundle bundles package without polyfills 1`] = `
-"(function (global) {
-  global.__DEV__ = false;
-  global.__BUNDLE_START_TIME__ = global.nativePerformanceNow ? global.nativePerformanceNow() : Date.now();
-  global.process = {
-    env: {
-      NODE_ENV: 'production'
-    }
-  };
-})(this);
+"var __DEV__=false,__BUNDLE_START_TIME__=this.nativePerformanceNow?nativePerformanceNow():Date.now(),process={env:{NODE_ENV:'production'}};
 (function (global) {
   'use strict';
 
diff --git a/packages/metro/src/lib/getPreludeCode.js b/packages/metro/src/lib/getPreludeCode.js
new file mode 100644
index 00000000..1807010f
--- /dev/null
+++ b/packages/metro/src/lib/getPreludeCode.js
@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ * @format
+ */
+
+'use strict';
+
+function getPreludeCode({isDev}: {|+isDev: boolean|}): string {
+  return (
+    `var __DEV__=${String(isDev)},` +
+    '__BUNDLE_START_TIME__=this.nativePerformanceNow?nativePerformanceNow():Date.now(),' +
+    `process={env:{NODE_ENV:'${isDev ? 'development' : 'production'}'}};`
+  );
+}
+
+module.exports = getPreludeCode;
diff --git a/packages/metro/src/lib/polyfills/prelude.js b/packages/metro/src/lib/polyfills/prelude.js
deleted file mode 100644
index 62493f86..00000000
--- a/packages/metro/src/lib/polyfills/prelude.js
+++ /dev/null
@@ -1,19 +0,0 @@
-/**
- * Copyright (c) 2013-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @polyfill
- * @format
- */
-
-global.__DEV__ = false;
-
-global.__BUNDLE_START_TIME__ = global.nativePerformanceNow
-  ? global.nativePerformanceNow()
-  : Date.now();
-
-global.process = {env: {NODE_ENV: 'production'}};
diff --git a/packages/metro/src/lib/polyfills/prelude_dev.js b/packages/metro/src/lib/polyfills/prelude_dev.js
deleted file mode 100644
index c615f723..00000000
--- a/packages/metro/src/lib/polyfills/prelude_dev.js
+++ /dev/null
@@ -1,19 +0,0 @@
-/**
- * Copyright (c) 2013-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @polyfill
- * @format
- */
-
-global.__DEV__ = true;
-
-global.__BUNDLE_START_TIME__ = global.nativePerformanceNow
-  ? global.nativePerformanceNow()
-  : Date.now();
-
-global.process = {env: {NODE_ENV: 'development'}};