diff --git a/packages/angular_devkit/build_angular/src/utils/environment-options.ts b/packages/angular_devkit/build_angular/src/utils/environment-options.ts
index 9db966c6171f..0ac0852244e1 100644
--- a/packages/angular_devkit/build_angular/src/utils/environment-options.ts
+++ b/packages/angular_devkit/build_angular/src/utils/environment-options.ts
@@ -78,8 +78,11 @@ export const allowMinify = debugOptimize.minify;
 const maxWorkersVariable = process.env['NG_BUILD_MAX_WORKERS'];
 export const maxWorkers = isPresent(maxWorkersVariable) ? +maxWorkersVariable : 4;
 
+// Default to enabled unless inside a Web Container which currently fails when transferring MessagePort objects
 const parallelTsVariable = process.env['NG_BUILD_PARALLEL_TS'];
-export const useParallelTs = !isPresent(parallelTsVariable) || !isDisabled(parallelTsVariable);
+export const useParallelTs = isPresent(parallelTsVariable)
+  ? !isDisabled(parallelTsVariable)
+  : !process.versions.webcontainer;
 
 const legacySassVariable = process.env['NG_BUILD_LEGACY_SASS'];
 export const useLegacySass: boolean = (() => {