diff --git a/packages/jest-util/src/__tests__/createProcessObject.test.ts b/packages/jest-util/src/__tests__/createProcessObject.test.ts
index 4eca00c977a2..baa29639c6c5 100644
--- a/packages/jest-util/src/__tests__/createProcessObject.test.ts
+++ b/packages/jest-util/src/__tests__/createProcessObject.test.ts
@@ -6,9 +6,17 @@
  */
 
 import EventEmitter from 'events';
-import createProcessObject from '../createProcessObject';
+
+let createProcessObject;
+
+function requireCreateProcessObject() {
+  jest.isolateModules(() => {
+    createProcessObject = require('../createProcessObject').default;
+  });
+}
 
 it('creates a process object that looks like the original one', () => {
+  requireCreateProcessObject();
   const fakeProcess = createProcessObject();
 
   // "process" inherits from EventEmitter through the prototype chain.
@@ -35,6 +43,7 @@ it('fakes require("process") so it is equal to "global.process"', () => {
 
 it('checks that process.env works as expected on Linux platforms', () => {
   Object.defineProperty(process, 'platform', {get: () => 'linux'});
+  requireCreateProcessObject();
 
   // Existing properties inside process.env are copied to the fake environment.
   process.env.PROP_STRING = 'foo';
@@ -73,6 +82,7 @@ it('checks that process.env works as expected on Linux platforms', () => {
 
 it('checks that process.env works as expected in Windows platforms', () => {
   Object.defineProperty(process, 'platform', {get: () => 'win32'});
+  requireCreateProcessObject();
 
   // Windows is not case sensitive when it comes to property names.
   process.env.PROP_STRING = 'foo';
diff --git a/packages/jest-util/src/createProcessObject.ts b/packages/jest-util/src/createProcessObject.ts
index 903336636bdd..53d18dd43cb5 100644
--- a/packages/jest-util/src/createProcessObject.ts
+++ b/packages/jest-util/src/createProcessObject.ts
@@ -8,6 +8,8 @@
 import deepCyclicCopy from './deepCyclicCopy';
 
 const BLACKLIST = new Set(['env', 'mainModule', '_events']);
+const isWin32 = process.platform === 'win32';
+const proto: Record<string, any> = Object.getPrototypeOf(process.env);
 
 // The "process.env" object has a bunch of particularities: first, it does not
 // directly extend from Object; second, it converts any assigned value to a
@@ -15,42 +17,51 @@ const BLACKLIST = new Set(['env', 'mainModule', '_events']);
 // mimic it (see https://nodejs.org/api/process.html#process_process_env).
 
 function createProcessEnv(): NodeJS.ProcessEnv {
-  if (typeof Proxy === 'undefined') {
-    return deepCyclicCopy(process.env);
-  }
-
-  const proto: Record<string, any> = Object.getPrototypeOf(process.env);
   const real = Object.create(proto);
   const lookup: typeof process.env = {};
 
-  const proxy = new Proxy(real, {
-    deleteProperty(_target, key) {
-      for (const name in real) {
-        if (real.hasOwnProperty(name)) {
-          if (typeof key === 'string' && process.platform === 'win32') {
-            if (name.toLowerCase() === key.toLowerCase()) {
-              delete real[name];
-              delete lookup[name.toLowerCase()];
-            }
-          } else {
-            if (key === name) {
-              delete real[name];
-              delete lookup[name];
-            }
+  function deletePropertyWin32(_target: any, key: any) {
+    for (const name in real) {
+      if (real.hasOwnProperty(name)) {
+        if (typeof key === 'string') {
+          if (name.toLowerCase() === key.toLowerCase()) {
+            delete real[name];
+            delete lookup[name.toLowerCase()];
+          }
+        } else {
+          if (key === name) {
+            delete real[name];
+            delete lookup[name];
           }
         }
       }
+    }
 
-      return true;
-    },
+    return true;
+  }
 
-    get(_target, key) {
-      if (typeof key === 'string' && process.platform === 'win32') {
-        return lookup[key in proto ? key : key.toLowerCase()];
-      } else {
-        return real[key];
-      }
-    },
+  function deleteProperty(_target: any, key: any) {
+    delete real[key];
+    delete lookup[key];
+
+    return true;
+  }
+
+  function getProperty(_target: any, key: any) {
+    return real[key];
+  }
+
+  function getPropertyWin32(_target: any, key: any) {
+    if (typeof key === 'string') {
+      return lookup[key in proto ? key : key.toLowerCase()];
+    } else {
+      return real[key];
+    }
+  }
+
+  const proxy = new Proxy(real, {
+    deleteProperty: isWin32 ? deletePropertyWin32 : deleteProperty,
+    get: isWin32 ? getPropertyWin32 : getProperty,
 
     set(_target, key, value) {
       const strValue = '' + value;