diff --git a/Libraries/Core/setUpGlobals.js b/Libraries/Core/setUpGlobals.js
index 4d740807dd156d..8ddff03bc66e78 100644
--- a/Libraries/Core/setUpGlobals.js
+++ b/Libraries/Core/setUpGlobals.js
@@ -15,18 +15,21 @@
  * You can use this module directly, or just require InitializeCore.
  */
 if (global.window === undefined) {
-  // $FlowFixMe[cannot-write]
+  // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
   global.window = global;
 }
 
 if (global.self === undefined) {
-  // $FlowFixMe[cannot-write]
+  // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
   global.self = global;
 }
 
 // Set up process
+// $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
 global.process = global.process || {};
+// $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
 global.process.env = global.process.env || {};
 if (!global.process.env.NODE_ENV) {
+  // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
   global.process.env.NODE_ENV = __DEV__ ? 'development' : 'production';
 }
diff --git a/Libraries/Core/setUpNavigator.js b/Libraries/Core/setUpNavigator.js
index 1dbe429aaea2a8..bcf2cbd597b5fb 100644
--- a/Libraries/Core/setUpNavigator.js
+++ b/Libraries/Core/setUpNavigator.js
@@ -12,10 +12,11 @@
 
 const {polyfillObjectProperty} = require('../Utilities/PolyfillFunctions');
 
-let navigator = global.navigator;
+const navigator = global.navigator;
 if (navigator === undefined) {
-  global.navigator = navigator = {};
+  // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
+  global.navigator = {product: 'ReactNative'};
+} else {
+  // see https://github.com/facebook/react-native/issues/10881
+  polyfillObjectProperty(navigator, 'product', () => 'ReactNative');
 }
-
-// see https://github.com/facebook/react-native/issues/10881
-polyfillObjectProperty(navigator, 'product', () => 'ReactNative');
diff --git a/Libraries/Core/setUpPerformance.js b/Libraries/Core/setUpPerformance.js
index c007370c6bb4f8..ef12f6c9ae1580 100644
--- a/Libraries/Core/setUpPerformance.js
+++ b/Libraries/Core/setUpPerformance.js
@@ -17,6 +17,7 @@ if (!global.performance) {
  * https://developer.mozilla.org/en-US/docs/Web/API/Performance/now
  */
 if (typeof global.performance.now !== 'function') {
+  // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
   global.performance.now = function () {
     const performanceNow = global.nativePerformanceNow || Date.now;
     return performanceNow();
diff --git a/Libraries/Core/setUpWebPerformance.js b/Libraries/Core/setUpWebPerformance.js
index 13475773d29dfc..333c5c57c1b03c 100644
--- a/Libraries/Core/setUpWebPerformance.js
+++ b/Libraries/Core/setUpWebPerformance.js
@@ -12,5 +12,6 @@ import Performance from '../WebPerformance/Performance';
 
 // TODO: Replace setUpPerformance with this once the WebPerformance API is stable (T143070419)
 export default function setUpPerformance() {
+  // $FlowExpectedError[cannot-write] The global isn't writable anywhere but here, where we define it.
   global.performance = new Performance();
 }
diff --git a/flow/global.js b/flow/global.js
index ee60a57fdb03cc..63624ca3d2dc16 100644
--- a/flow/global.js
+++ b/flow/global.js
@@ -19,8 +19,19 @@ declare var global: {
   // setUpGlobals
   +window: typeof global,
   +self: typeof global,
+  +process: {
+    +env: {
+      +NODE_ENV: 'development' | 'production',
+    },
+    +argv?: $ReadOnlyArray<string>,
+  },
 
-  // setXHR
+  // setUpPerformance
+  +performance: {
+    +now: () => number,
+  },
+
+  // setUpXHR
   +XMLHttpRequest: typeof XMLHttpRequest,
   +FormData: typeof FormData,
   +fetch: typeof fetch,
@@ -39,17 +50,27 @@ declare var global: {
   // setUpAlert
   +alert: typeof alert,
 
+  // setUpNavigator
+  +navigator: {
+    +product: 'ReactNative',
+    +appName?: ?string,
+    ...
+  },
+
   // setUpTimers
-  +clearInterval: typeof clearInterval,
-  +clearTimeout: typeof clearTimeout,
   +setInterval: typeof setInterval,
+  +clearInterval: typeof clearInterval,
   +setTimeout: typeof setTimeout,
+  +clearTimeout: typeof clearTimeout,
   +requestAnimationFrame: typeof requestAnimationFrame,
   +cancelAnimationFrame: typeof cancelAnimationFrame,
   +requestIdleCallback: typeof requestIdleCallback,
   +cancelIdleCallback: typeof cancelIdleCallback,
-  +setTimeout: typeof setTimeout,
   +queueMicrotask: typeof queueMicrotask,
+  +setImmediate: typeof setImmediate,
+  +clearImmediate: typeof clearImmediate,
+
+  // Polyfills
   +console: typeof console,
 
   // JavaScript environments specific