diff --git a/packages/techdocs-common/__mocks__/aws-sdk.ts b/packages/techdocs-common/__mocks__/aws-sdk.ts
index b956b4309a..b546494118 100644
--- a/packages/techdocs-common/__mocks__/aws-sdk.ts
+++ b/packages/techdocs-common/__mocks__/aws-sdk.ts
@@ -15,7 +15,28 @@
  */
 import type { S3 as S3Types } from 'aws-sdk';
 import { EventEmitter } from 'events';
-import fs from 'fs';
+import fs from 'fs-extra';
+import os from 'os';
+import path from 'path';
+
+const rootDir = os.platform() === 'win32' ? 'C:\\rootDir' : '/rootDir';
+
+/**
+ * @param Key Contains either / or \ as file separator depending upon OS.
+ */
+const checkFileExists = async (Key: string): Promise<boolean> => {
+  // Key will always have / as file separator irrespective of OS since S3 expects /.
+  // Normalize Key to OS specific path before checking if file exists.
+  const relativeFilePath = Key.split(path.posix.sep).join(path.sep);
+  const filePath = path.join(rootDir, Key);
+
+  try {
+    await fs.access(filePath, fs.constants.F_OK);
+    return true;
+  } catch (err) {
+    return false;
+  }
+};
 
 export class S3 {
   private readonly options;
@@ -26,22 +47,27 @@ export class S3 {
 
   headObject({ Key }: { Key: string }) {
     return {
-      promise: () => this.checkFileExists(Key),
+      promise: async () => {
+        if (!(await checkFileExists(Key))) {
+          throw new Error('File does not exist');
+        }
+      },
     };
   }
 
   getObject({ Key }: { Key: string }) {
+    const filePath = path.join(rootDir, Key);
     return {
-      promise: () => this.checkFileExists(Key),
+      promise: () => checkFileExists(filePath),
       createReadStream: () => {
         const emitter = new EventEmitter();
         process.nextTick(() => {
-          if (fs.existsSync(Key)) {
-            emitter.emit('data', Buffer.from(fs.readFileSync(Key)));
+          if (fs.existsSync(filePath)) {
+            emitter.emit('data', Buffer.from(fs.readFileSync(filePath)));
           } else {
             emitter.emit(
               'error',
-              new Error(`The file ${Key} does not exist !`),
+              new Error(`The file ${filePath} does not exist !`),
             );
           }
           emitter.emit('end');
@@ -51,16 +77,6 @@ export class S3 {
     };
   }
 
-  checkFileExists(Key: string) {
-    return new Promise((resolve, reject) => {
-      if (fs.existsSync(Key)) {
-        resolve('');
-      } else {
-        reject({ message: 'The object does not exist !' });
-      }
-    });
-  }
-
   headBucket() {
     return new Promise(resolve => {
       resolve('');
@@ -70,9 +86,9 @@ export class S3 {
   upload({ Key }: { Key: string }) {
     return {
       promise: () =>
-        new Promise((resolve, reject) => {
-          if (!fs.existsSync(Key)) {
-            reject('');
+        new Promise(async (resolve, reject) => {
+          if (!(await checkFileExists(Key))) {
+            reject(`The file ${Key} does not exist`);
           } else {
             resolve('');
           }
diff --git a/packages/techdocs-common/src/stages/publish/awsS3.test.ts b/packages/techdocs-common/src/stages/publish/awsS3.test.ts
index 9376e74e92..bf029dd7db 100644
--- a/packages/techdocs-common/src/stages/publish/awsS3.test.ts
+++ b/packages/techdocs-common/src/stages/publish/awsS3.test.ts
@@ -16,7 +16,8 @@
 import type { Entity, EntityName } from '@backstage/catalog-model';
 import { ConfigReader } from '@backstage/config';
 import mockFs from 'mock-fs';
-import path from 'path';
+import * as os from 'os';
+import * as path from 'path';
 import * as winston from 'winston';
 import { AwsS3Publish } from './awsS3';
 import { PublisherBase, TechDocsMetadata } from './types';
@@ -41,13 +42,15 @@ const createMockEntityName = (): EntityName => ({
   namespace: 'test-namespace',
 });
 
+const rootDir = os.platform() === 'win32' ? 'C:\\rootDir' : '/rootDir';
+
 const getEntityRootDir = (entity: Entity) => {
   const {
     kind,
     metadata: { namespace, name },
   } = entity;
-  const entityRootDir = path.join(namespace as string, kind, name);
-  return entityRootDir;
+
+  return path.join(rootDir, namespace as string, kind, name);
 };
 
 const logger = winston.createLogger();
@@ -57,6 +60,7 @@ jest.spyOn(logger, 'error').mockReturnValue(logger);
 let publisher: PublisherBase;
 
 beforeEach(() => {
+  mockFs.restore();
   const mockConfig = new ConfigReader({
     techdocs: {
       requestUrl: 'http://localhost:7000',
@@ -78,6 +82,10 @@ beforeEach(() => {
 
 describe('AwsS3Publish', () => {
   describe('publish', () => {
+    afterEach(() => {
+      mockFs.restore();
+    });
+
     it('should publish a directory', async () => {
       const entity = createMockEntity();
       const entityRootDir = getEntityRootDir(entity);
@@ -98,11 +106,11 @@ describe('AwsS3Publish', () => {
           directory: entityRootDir,
         }),
       ).toBeUndefined();
-      mockFs.restore();
     });
 
     it('should fail to publish a directory', async () => {
       const wrongPathToGeneratedDirectory = path.join(
+        rootDir,
         'wrong',
         'path',
         'to',
@@ -126,13 +134,18 @@ describe('AwsS3Publish', () => {
           entity,
           directory: wrongPathToGeneratedDirectory,
         })
-        .catch(error =>
-          expect(error).toEqual(
-            new Error(
-              `Unable to upload file(s) to AWS S3. Error Failed to read template directory: ENOENT, no such file or directory '${wrongPathToGeneratedDirectory}'`,
+        .catch(error => {
+          expect(error.message).toEqual(
+            // Can not do exact error message match due to mockFs adding unexpected characters in the path when throwing the error
+            // Issue reported https://github.com/tschaub/mock-fs/issues/118
+            expect.stringContaining(
+              `Unable to upload file(s) to AWS S3. Error Failed to read template directory: ENOENT, no such file or directory`,
             ),
-          ),
-        );
+          );
+          expect(error.message).toEqual(
+            expect.stringContaining(wrongPathToGeneratedDirectory),
+          );
+        });
       mockFs.restore();
     });
   });
diff --git a/packages/techdocs-common/src/stages/publish/awsS3.ts b/packages/techdocs-common/src/stages/publish/awsS3.ts
index b0b29e8654..6145ec6365 100644
--- a/packages/techdocs-common/src/stages/publish/awsS3.ts
+++ b/packages/techdocs-common/src/stages/publish/awsS3.ts
@@ -140,9 +140,17 @@ export class AwsS3Publish implements PublisherBase {
         // Remove the absolute path prefix of the source directory
         // Path of all files to upload, relative to the root of the source directory
         // e.g. ['index.html', 'sub-page/index.html', 'assets/images/favicon.png']
-        const relativeFilePath = filePath.replace(`${directory}/`, '');
+        const relativeFilePath = path.relative(directory, filePath);
+
+        // Convert destination file path to a POSIX path for uploading.
+        // S3 expects / as path separator and relativeFilePath will contain \\ on Windows.
+        // https://docs.aws.amazon.com/AmazonS3/latest/userguide/object-keys.html
+        const relativeFilePathPosix = relativeFilePath
+          .split(path.sep)
+          .join(path.posix.sep);
+
         const entityRootDir = `${entity.metadata.namespace}/${entity.kind}/${entity.metadata.name}`;
-        const destination = `${entityRootDir}/${relativeFilePath}`; // S3 Bucket file relative path
+        const destination = `${entityRootDir}/${relativeFilePathPosix}`; // S3 Bucket file relative path
 
         const fileContent = await fs.readFile(filePath, 'utf8');