diff --git a/build/azure-pipelines/mixin.js b/build/azure-pipelines/mixin.js
index efb7d4d1ca9..80409d54ec7 100644
--- a/build/azure-pipelines/mixin.js
+++ b/build/azure-pipelines/mixin.js
@@ -12,6 +12,8 @@ const es = require('event-stream');
 const vfs = require('vinyl-fs');
 const fancyLog = require('fancy-log');
 const ansiColors = require('ansi-colors');
+const fs = require('fs');
+const path = require('path');
 
 function main() {
 	const quality = process.env['VSCODE_QUALITY'];
@@ -21,7 +23,7 @@ function main() {
 		return;
 	}
 
-	const productJsonFilter = filter('product.json', { restore: true });
+	const productJsonFilter = filter(f => f.relative === 'product.json', { restore: true });
 
 	fancyLog(ansiColors.blue('[mixin]'), `Mixing in sources:`);
 	return vfs
@@ -29,7 +31,32 @@ function main() {
 		.pipe(filter(f => !f.isDirectory()))
 		.pipe(productJsonFilter)
 		.pipe(buffer())
-		.pipe(json(o => Object.assign({}, require('../product.json'), o)))
+		.pipe(json(o => {
+			const ossProduct = JSON.parse(fs.readFileSync(path.join(__dirname, '..', '..', 'product.json'), 'utf8'));
+			let builtInExtensions = ossProduct.builtInExtensions;
+
+			if (Array.isArray(o.builtInExtensions)) {
+				fancyLog(ansiColors.blue('[mixin]'), 'Overwriting built-in extensions:', o.builtInExtensions.map(e => e.name));
+
+				builtInExtensions = o.builtInExtensions;
+			} else if (o.builtInExtensions) {
+				const include = o.builtInExtensions['include'] || [];
+				const exclude = o.builtInExtensions['exclude'] || [];
+
+				fancyLog(ansiColors.blue('[mixin]'), 'OSS built-in extensions:', builtInExtensions.map(e => e.name));
+				fancyLog(ansiColors.blue('[mixin]'), 'Including built-in extensions:', include.map(e => e.name));
+				fancyLog(ansiColors.blue('[mixin]'), 'Excluding built-in extensions:', exclude);
+
+				builtInExtensions = builtInExtensions.filter(ext => !include.find(e => e.name === ext.name) && !exclude.find(name => name === ext.name));
+				builtInExtensions = [...builtInExtensions, ...include];
+
+				fancyLog(ansiColors.blue('[mixin]'), 'Final built-in extensions:', builtInExtensions.map(e => e.name));
+			} else {
+				fancyLog(ansiColors.blue('[mixin]'), 'Inheriting OSS built-in extensions', builtInExtensions.map(e => e.name));
+			}
+
+			return { ...ossProduct, builtInExtensions };
+		}))
 		.pipe(productJsonFilter.restore)
 		.pipe(es.mapSync(function (f) {
 			fancyLog(ansiColors.blue('[mixin]'), f.relative, ansiColors.green('✔︎'));
@@ -38,4 +65,4 @@ function main() {
 		.pipe(vfs.dest('.'));
 }
 
-main();
\ No newline at end of file
+main();