diff --git a/packages/metro-bundler/src/ModuleGraph/ModuleGraph.js b/packages/metro-bundler/src/ModuleGraph/ModuleGraph.js
index 757fe16f..9d67a024 100644
--- a/packages/metro-bundler/src/ModuleGraph/ModuleGraph.js
+++ b/packages/metro-bundler/src/ModuleGraph/ModuleGraph.js
@@ -27,7 +27,7 @@ import type {
 type BuildFn = (
   entryPoints: Iterable<string>,
   options: BuildOptions,
-  callback: Callback<{modules: Iterable<Module>, entryModules: Iterable<Module>}>,
+  callback: Callback<GraphResult>,
 ) => void;
 
 type BuildOptions = {|
diff --git a/packages/metro-bundler/src/ModuleGraph/types.flow.js b/packages/metro-bundler/src/ModuleGraph/types.flow.js
index aedf1e08..dd105630 100644
--- a/packages/metro-bundler/src/ModuleGraph/types.flow.js
+++ b/packages/metro-bundler/src/ModuleGraph/types.flow.js
@@ -46,8 +46,8 @@ type GraphOptions = {|
 |};
 
 export type GraphResult = {|
-  entryModules: Array<Module>,
-  modules: Array<Module>,
+  entryModules: Iterable<Module>,
+  modules: Iterable<Module>,
 |};
 
 export type IdForPathFn = {path: string} => number;