diff --git a/README.md b/README.md
index 04b83e3..2de539c 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,10 @@ language servers written in TS and JS. It also contains helper methods to conver
 [![NPM Version](https://img.shields.io/npm/v/vscode-nls-dev.svg)](https://npmjs.org/package/vscode-nls-dev)
 [![NPM Downloads](https://img.shields.io/npm/dm/vscode-nls-dev.svg)](https://npmjs.org/package/vscode-nls-dev)
 
+### 4.0.1
+
+* [Allow overriding of baseDir in proccessing files.](https://github.com/microsoft/vscode-nls-dev/pull/41)
+
 ### 4.0.0-next.1
 
 * [Add support for comments in messages (e.g. package.nls.json)](https://github.com/microsoft/vscode-nls-dev/issues/32)
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index cf005dd..951ab14 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -13,12 +13,12 @@ jobs:
 
 - job: Windows
   pool:
-    vmImage: VS2017-Win2016
+    vmImage: 'windows-latest'
   steps:
   - template: build/azure-pipelines/win32/build.yml
 
 - job: Indexing
   pool:
-    vmImage: VS2017-Win2016
+    vmImage: 'windows-latest'
   steps:
   - template: build/azure-pipelines/index/build.yml
\ No newline at end of file
diff --git a/package-lock.json b/package-lock.json
index 05b5ea7..c919afd 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
 	"name": "vscode-nls-dev",
-	"version": "4.0.0",
+	"version": "4.0.1",
 	"lockfileVersion": 2,
 	"requires": true,
 	"packages": {
 		"": {
 			"name": "vscode-nls-dev",
-			"version": "4.0.0",
+			"version": "4.0.1",
 			"license": "MIT",
 			"dependencies": {
 				"ansi-colors": "^4.1.1",
diff --git a/package.json b/package.json
index 19f5072..46426f5 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "vscode-nls-dev",
-	"version": "4.0.0",
+	"version": "4.0.1",
 	"description": "Development time npm module to generate strings bundles from Javascript files",
 	"author": "Microsoft Corporation",
 	"license": "MIT",
diff --git a/src/lib.ts b/src/lib.ts
index d659369..62041a1 100644
--- a/src/lib.ts
+++ b/src/lib.ts
@@ -347,7 +347,7 @@ class TextModel {
 	}
 }
 
-function analyze(contents: string, relativeFilename: string | undefined, options: ts.CompilerOptions = {}): AnalysisResult {
+function analyze(contents: string, relativeFilename?: string, baseDir?: string, options: ts.CompilerOptions = {}): AnalysisResult {
 
 	const vscodeRegExp = /^\s*(["'])vscode-nls\1\s*$/;
 
@@ -553,9 +553,10 @@ function analyze(contents: string, relativeFilename: string | undefined, options
 	loadCalls.reduce((memo, loadCall) => {
 		if (loadCall.arguments.length === 0) {
 			const args = loadCall.arguments;
+			const dir = baseDir ? JSON.stringify(baseDir) : '__dirname';
 			patches.push({
 				span: { start: ts.getLineAndCharacterOfPosition(sourceFile, args.pos), end: ts.getLineAndCharacterOfPosition(sourceFile, args.end) },
-				content: relativeFilename ? `require('path').join(__dirname, '${relativeFilename.replace(/\\/g, '\\\\')}')` : '__filename',
+				content: relativeFilename ? `require('path').join(${dir}, '${relativeFilename.replace(/\\/g, '\\\\')}')` : '__filename',
 			});
 		}
 		return memo;
@@ -640,9 +641,8 @@ function analyze(contents: string, relativeFilename: string | undefined, options
 	};
 }
 
-export function processFile(contents: string, relativeFileName: string | undefined, sourceMap?: string | RawSourceMap): { contents: string | undefined, sourceMap: string | undefined, bundle: JavaScriptMessageBundle | undefined, errors: string[] } {
-
-	const analysisResult = analyze(contents, relativeFileName);
+export function processFile(contents: string, relativeFileName?: string, baseDir?: string, sourceMap?: string | RawSourceMap): { contents?: string, sourceMap?: string, bundle?: JavaScriptMessageBundle, errors: string[] } {
+	const analysisResult = analyze(contents, relativeFileName, baseDir);
 	if (analysisResult.patches.length === 0) {
 		return {
 			contents: undefined,
diff --git a/src/main.ts b/src/main.ts
index 4a05893..5823583 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -40,7 +40,7 @@ export function rewriteLocalizeCalls(): ThroughStream {
 			const content = buffer.toString('utf8');
 			const sourceMap = file.sourceMap;
 
-			const result = processFile(content, undefined, sourceMap);
+			const result = processFile(content, undefined, undefined, sourceMap);
 			let messagesFile: File | undefined;
 			let metaDataFile: File | undefined;
 			if (result.errors && result.errors.length > 0) {
@@ -89,7 +89,7 @@ export function createMetaDataFiles(): ThroughStream {
 				return;
 			}
 
-			let result = processFile(file.contents.toString('utf8'), undefined, undefined);
+			let result = processFile(file.contents.toString('utf8'));
 			if (result.errors && result.errors.length > 0) {
 				result.errors.forEach(error => console.error(`${file.relative}${error}`));
 				this.emit('error', `Failed to rewrite file: ${file.path}`);
diff --git a/src/tests/analyze.tests.ts b/src/tests/analyze.tests.ts
index 4a37a38..5588b94 100644
--- a/src/tests/analyze.tests.ts
+++ b/src/tests/analyze.tests.ts
@@ -23,7 +23,7 @@ suite('Localize', () => {
 			'localize(0, null, \'Hello\', \'World\');',
 			'//# sourceMappingURL=test.js.map'
 		];
-		let result = nlsDev.processFile(code.join('\r\n'), undefined, sourceMap);
+		let result = nlsDev.processFile(code.join('\r\n'), undefined, undefined, sourceMap);
 
 		assert.strictEqual(result.contents, expected.join('\r\n'));
 		assert.strictEqual(result.sourceMap, '{"version":3,"sources":["test.ts"],"names":[],"mappings":"AAAA,IAAY,GAAG,WAAM,YAAY,CAAC,CAAA;AAClC,IAAI,QAAQ,GAAG,GAAG,CAAC,MAAM,CAAC,EAAE,MAAM,EAAE,OAAO,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,YAAE,CAAC;AAC9D,QAAQ,CAAC,aAAyB,EAAE,OAAO,CAAC,CAAC","sourceRoot":""}');
@@ -53,7 +53,7 @@ suite('Localize', () => {
 			'localize(0, null, \'Hello\', \'World\');',
 			'//# sourceMappingURL=test.js.map'
 		];
-		let result = nlsDev.processFile(code.join('\r\n'), undefined, sourceMap);
+		let result = nlsDev.processFile(code.join('\r\n'), undefined, undefined, sourceMap);
 		assert.strictEqual(result.contents, expected.join('\r\n'));
 		assert.strictEqual(result.sourceMap, '{"version":3,"sources":["test.ts"],"names":[],"mappings":"AAAA,IAAY,GAAG,WAAM,YAAY,CAAC,CAAA;AAClC,IAAI,QAAQ,GAAG,GAAG,CAAC,MAAM,CAAC,EAAE,MAAM,EAAE,OAAO,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,YAAE,CAAC;AAC9D,QAAQ,CAAC,CAGR,EAAE,IAAS,EAAE,OAAO,EAAE,OAAO,CAAC,CAAC","sourceRoot":""}');
 		assert.deepStrictEqual(result.bundle, {
@@ -143,6 +143,20 @@ suite('Localize', () => {
 		assert.strictEqual(result.contents, expected.join('\n'));
 	});
 
+	test('allows overriding base directory', ()	=> {
+		let code: string[] = [
+			'const nls = __importStar(require(\'vscode-nls\'))',
+			'var localize = nls.loadMessageBundle();',
+			'localize(\'keyOne\', \'{0} {1}\', \'Hello\', \'World\');'
+		];
+		let result = nlsDev.processFile(code.join('\n'), 'foo.js', '/');
+		let expected: string[] = [
+			'const nls = __importStar(require(\'vscode-nls\'))',
+			'var localize = nls.loadMessageBundle(require(\'path\').join("/", \'foo.js\'));',
+			'localize(0, null, \'Hello\', \'World\');'
+		];
+		assert.strictEqual(result.contents, expected.join('\n'));
+	});
 
 	test('https://github.com/Microsoft/vscode/issues/56792', () => {
 		let code: string[] = [
diff --git a/src/vscl.ts b/src/vscl.ts
index 9433139..59d2df5 100644
--- a/src/vscl.ts
+++ b/src/vscl.ts
@@ -80,7 +80,7 @@ argv._.forEach(element => {
 			}
 
 			const relativeFilename = keepFilenames && rootDir ? path.relative(rootDir, resolvedFile) : undefined;
-			const result = processFile(contents, relativeFilename, sourceMapContent);
+			const result = processFile(contents, relativeFilename, undefined, sourceMapContent);
 
 			if (result.errors && result.errors.length > 0) {
 				result.errors.forEach(error => console.error(`${file}${error}`));
diff --git a/src/webpack-loader.ts b/src/webpack-loader.ts
index b3e94c2..23c929c 100644
--- a/src/webpack-loader.ts
+++ b/src/webpack-loader.ts
@@ -17,7 +17,11 @@ module.exports = function (this: any, content: any, map: any, meta: any) {
 
 	const callback = this.async();
 	const relativePath = relative(this.query.base, this.resourcePath);
-	const result = processFile(content, relativePath, map);
+	const result = processFile(
+		content,
+		relativePath,
+		this.target === 'webworker' || this.target === 'web' ? '/' : undefined,
+		map);
 
 	if (result.errors && result.errors.length > 0) {
 		// error