diff --git a/packages/next/build/webpack/plugins/pages-manifest-plugin.js b/packages/next/build/webpack/plugins/pages-manifest-plugin.js
index b7ac3550e190c..918b3b2c508d7 100644
--- a/packages/next/build/webpack/plugins/pages-manifest-plugin.js
+++ b/packages/next/build/webpack/plugins/pages-manifest-plugin.js
@@ -23,7 +23,8 @@ export default class PagesManifestPlugin {
         }
 
         const {name} = entry
-        pages[`/${pagePath.replace(/\\/g, '/')}`] = name
+        // Write filename, replace any backslashes in path (on windows) with forwardslashes for cross-platform consistency.
+        pages[`/${pagePath.replace(/\\/g, '/')}`] = name.replace(/\\/g, '/')
       }
 
       if (typeof pages['/index'] !== 'undefined') {
diff --git a/test/integration/production/test/index.test.js b/test/integration/production/test/index.test.js
index e5c475f0aa6d8..757a7c6053688 100644
--- a/test/integration/production/test/index.test.js
+++ b/test/integration/production/test/index.test.js
@@ -16,7 +16,7 @@ import fetch from 'node-fetch'
 import dynamicImportTests from './dynamic'
 import processEnv from './process-env'
 import security from './security'
-import {BUILD_MANIFEST, REACT_LOADABLE_MANIFEST} from 'next-server/constants'
+import {BUILD_MANIFEST, REACT_LOADABLE_MANIFEST, PAGES_MANIFEST} from 'next-server/constants'
 
 const appDir = join(__dirname, '../')
 let appPort
@@ -319,6 +319,17 @@ describe('Production Usage', () => {
     expect(serverSideJsBody).toMatch(/404/)
   })
 
+  it('should not put backslashes in pages-manifest.json', () => {
+    // Whatever platform you build on, pages-manifest.json should use forward slash (/)
+    // See: https://github.com/zeit/next.js/issues/4920
+    const pagesManifest = require(join('..', '.next', 'server', PAGES_MANIFEST))
+
+    for (let key of Object.keys(pagesManifest)) {
+      expect(key).not.toMatch(/\\/)
+      expect(pagesManifest[key]).not.toMatch(/\\/)
+    }
+  })
+
   it('should handle failed param decoding', async () => {
     const html = await renderViaHTTP(appPort, '/%DE~%C7%1fY/')
     expect(html).toMatch(/400/)