diff --git a/packages/jest-runtime/src/cli/index.js b/packages/jest-runtime/src/cli/index.js
index 8deebe378335..a81a2d7da629 100644
--- a/packages/jest-runtime/src/cli/index.js
+++ b/packages/jest-runtime/src/cli/index.js
@@ -76,7 +76,7 @@ export function run(cliArgv?: Argv, cliInfo?: Array<string>) {
     unmockedModulePathPatterns: null,
   });
   Runtime.createContext(config, {
-    maxWorkers: os.cpus().length - 1,
+    maxWorkers: Math.max(os.cpus().length - 1, 1),
     watchman: globalConfig.watchman,
   })
     .then(hasteMap => {
diff --git a/packages/jest-worker/src/index.js b/packages/jest-worker/src/index.js
index 0b787d7e57b6..0cb636c2fc6c 100644
--- a/packages/jest-worker/src/index.js
+++ b/packages/jest-worker/src/index.js
@@ -57,7 +57,7 @@ export default class {
   _offset: number;
 
   constructor(workerPath: string, options?: FarmOptions = {}) {
-    const numWorkers = options.numWorkers || os.cpus().length - 1;
+    const numWorkers = options.numWorkers || Math.max(os.cpus().length - 1, 1);
     const workers = new Array(numWorkers);
     const stdout = mergeStream();
     const stderr = mergeStream();