diff --git a/src/__tests__/process.test.ts b/src/__tests__/process.test.ts
index 71c1e6aaa..abe78440f 100644
--- a/src/__tests__/process.test.ts
+++ b/src/__tests__/process.test.ts
@@ -7,8 +7,8 @@ describe('process', () => {
       expect(typeof _process).toBe('object');
     });
     it('.getuid() and .getgid()', () => {
-      expect(typeof proc.getuid()).toBe('number');
-      expect(typeof proc.getgid()).toBe('number');
+      expect(typeof proc.getuid?.() ?? 0).toBe('number');
+      expect(typeof proc.getgid?.() ?? 0).toBe('number');
     });
     it('.cwd()', () => {
       expect(typeof proc.cwd()).toBe('string');
diff --git a/src/node.ts b/src/node.ts
index c55715ecc..df8f1c107 100644
--- a/src/node.ts
+++ b/src/node.ts
@@ -6,6 +6,8 @@ import { EventEmitter } from 'events';
 import Stats from './Stats';
 
 const { S_IFMT, S_IFDIR, S_IFREG, S_IFLNK, O_APPEND } = constants;
+const getuid = (): number => process.getuid?.() ?? 0;
+const getgid = (): number => process.getgid?.() ?? 0;
 
 export const SEP = '/';
 
@@ -17,8 +19,8 @@ export class Node extends EventEmitter {
   ino: number;
 
   // User ID and group ID.
-  uid: number = process.getuid();
-  gid: number = process.getgid();
+  uid: number = getuid();
+  gid: number = getgid();
 
   atime = new Date();
   mtime = new Date();
@@ -167,7 +169,7 @@ export class Node extends EventEmitter {
     this.emit('change', this);
   }
 
-  canRead(uid: number = process.getuid(), gid: number = process.getgid()): boolean {
+  canRead(uid: number = getuid(), gid: number = getgid()): boolean {
     if (this.perm & S.IROTH) {
       return true;
     }
@@ -187,7 +189,7 @@ export class Node extends EventEmitter {
     return false;
   }
 
-  canWrite(uid: number = process.getuid(), gid: number = process.getgid()): boolean {
+  canWrite(uid: number = getuid(), gid: number = getgid()): boolean {
     if (this.perm & S.IWOTH) {
       return true;
     }
diff --git a/src/process.ts b/src/process.ts
index 26db6cfb6..1cbdf24e6 100644
--- a/src/process.ts
+++ b/src/process.ts
@@ -1,9 +1,9 @@
 // Here we mock the global `process` variable in case we are not in Node's environment.
 
 export interface IProcess {
-  getuid(): number;
+  getuid?(): number;
 
-  getgid(): number;
+  getgid?(): number;
 
   cwd(): string;
 
@@ -38,8 +38,6 @@ const maybeReturnProcess = (): IProcess | undefined => {
 export function createProcess(): IProcess {
   const p: IProcess = maybeReturnProcess() || ({} as IProcess);
 
-  if (!p.getuid) p.getuid = () => 0;
-  if (!p.getgid) p.getgid = () => 0;
   if (!p.cwd) p.cwd = () => '/';
   if (!p.nextTick) p.nextTick = require('./setImmediate').default;
   if (!p.emitWarning)