diff --git a/packages/metro-bundler/src/ModuleGraph/ModuleGraph.js b/packages/metro-bundler/src/ModuleGraph/ModuleGraph.js
index 2c6c905e..4518ca50 100644
--- a/packages/metro-bundler/src/ModuleGraph/ModuleGraph.js
+++ b/packages/metro-bundler/src/ModuleGraph/ModuleGraph.js
@@ -92,7 +92,7 @@ exports.createBuildSetup = (
       const prependedScripts = [preludeScript, ...moduleSystem, ...polyfills];
       callback(null, {
         entryModules,
-        modules: concat(prependedScripts, modules),
+        modules: prependedScripts.concat(modules),
         prependedScripts,
       });
     });
diff --git a/packages/metro-bundler/src/ModuleGraph/__tests__/ModuleGraph-test.js b/packages/metro-bundler/src/ModuleGraph/__tests__/ModuleGraph-test.js
index 352e3e2f..9607ae20 100644
--- a/packages/metro-bundler/src/ModuleGraph/__tests__/ModuleGraph-test.js
+++ b/packages/metro-bundler/src/ModuleGraph/__tests__/ModuleGraph-test.js
@@ -68,7 +68,7 @@ describe('build setup', () => {
   it('places polyfills after the module system', done => {
     buildSetup(noEntryPoints, polyfillOptions, (error, result) => {
       const list = polyfillOptions.getPolyfills();
-      const polyfills = Array.from(result.modules).slice(2, list.length + 2);
+      const polyfills = result.modules.slice(2, list.length + 2);
       expect(polyfills).toEqual(list.map(moduleFromPath));
       done();
     });
@@ -77,7 +77,7 @@ describe('build setup', () => {
   it('places all entry points and dependencies at the end, post-processed', done => {
     const entryPoints = ['b', 'c', 'd'];
     buildSetup(entryPoints, noOptions, (error, result) => {
-      expect(Array.from(result.modules).slice(-4))
+      expect(result.modules.slice(-4))
         .toEqual(['a', 'b', 'c', 'd'].map(moduleFromPath));
       done();
     });
diff --git a/packages/metro-bundler/src/ModuleGraph/types.flow.js b/packages/metro-bundler/src/ModuleGraph/types.flow.js
index 6db31c26..12496a74 100644
--- a/packages/metro-bundler/src/ModuleGraph/types.flow.js
+++ b/packages/metro-bundler/src/ModuleGraph/types.flow.js
@@ -52,8 +52,8 @@ type GraphOptions = {|
 |};
 
 export type GraphResult = {|
-  entryModules: Iterable<Module>,
-  modules: Iterable<Module>,
+  entryModules: $ReadOnlyArray<Module>,
+  modules: $ReadOnlyArray<Module>,
 |};
 
 export type IdForPathFn = {path: string} => number;
@@ -163,7 +163,11 @@ export type LibraryOptions = {|
 |};
 
 export type Base64Content = string;
-export type AssetContentsByPath = {[destFilePath: string]: Base64Content};
+export type AssetContents = {
+  +data: Base64Content,
+  +outputPath: string,
+};
+export type AssetContentsByPath = {+[moduleFilePath: string]: $ReadOnlyArray<AssetContents>};
 
 export type Library = {|
   +files: Array<TransformedCodeFile>,