diff --git a/packages/metro-bundler/src/ModuleGraph/output/__tests__/multiple-files-ram-bundle-test.js b/packages/metro-bundler/src/ModuleGraph/output/__tests__/multiple-files-ram-bundle-test.js
index 2cbe51fa..79152eea 100644
--- a/packages/metro-bundler/src/ModuleGraph/output/__tests__/multiple-files-ram-bundle-test.js
+++ b/packages/metro-bundler/src/ModuleGraph/output/__tests__/multiple-files-ram-bundle-test.js
@@ -70,9 +70,11 @@ it('creates a source map', () => {
 it('creates a magic file with the number', () => {
   expect(extraFiles).toBeDefined();
   // $FlowFixMe "extraFiles" is always defined at this point.
-  expect(extraFiles.get('UNBUNDLE')).toBeDefined();
+  expect(extraFiles.get('js-modules/UNBUNDLE')).toBeDefined();
   // $FlowFixMe "extraFiles" is always defined at this point.
-  expect(extraFiles.get('UNBUNDLE').readUInt32LE(0)).toBe(0xfb0bd1e5);
+  expect(extraFiles.get('js-modules/UNBUNDLE').readUInt32LE(0)).toBe(
+    0xfb0bd1e5,
+  );
 });
 
 it('bundles each file separately', () => {
diff --git a/packages/metro-bundler/src/ModuleGraph/output/multiple-files-ram-bundle.js b/packages/metro-bundler/src/ModuleGraph/output/multiple-files-ram-bundle.js
index 8063931d..711067c8 100644
--- a/packages/metro-bundler/src/ModuleGraph/output/multiple-files-ram-bundle.js
+++ b/packages/metro-bundler/src/ModuleGraph/output/multiple-files-ram-bundle.js
@@ -50,7 +50,10 @@ function asMultipleFilesRamBundle({
 
   // Prepare and write magic number file.
   magicFileContents.writeUInt32LE(MAGIC_UNBUNDLE_NUMBER, 0);
-  extraFiles.set(MAGIC_UNBUNDLE_FILENAME, magicFileContents);
+  extraFiles.set(
+    path.join(JS_MODULES, MAGIC_UNBUNDLE_FILENAME),
+    magicFileContents,
+  );
 
   // Create the source map (with no module groups, as they are ignored).
   const map = buildSourceMapWithMetaData({