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 c1e330b37963..9d53be82ce79 100644
--- a/packages/angular_devkit/build_angular/src/utils/environment-options.ts
+++ b/packages/angular_devkit/build_angular/src/utils/environment-options.ts
@@ -78,7 +78,7 @@ export const allowMinify = debugOptimize.minify;
 const maxWorkersVariable = process.env['NG_BUILD_MAX_WORKERS'];
 export const maxWorkers = isPresent(maxWorkersVariable)
   ? +maxWorkersVariable
-  : Math.min(4, availableParallelism());
+  : Math.min(4, Math.max(availableParallelism() - 1, 1));
 
 const parallelTsVariable = process.env['NG_BUILD_PARALLEL_TS'];
 export const useParallelTs = !isPresent(parallelTsVariable) || !isDisabled(parallelTsVariable);