diff --git a/packages/jest-cli/src/runTest.js b/packages/jest-cli/src/runTest.js
index 31f55f150c16..9c8720fabd77 100644
--- a/packages/jest-cli/src/runTest.js
+++ b/packages/jest-cli/src/runTest.js
@@ -67,8 +67,9 @@ function runTest(path: Path, config: Config, resolver: Resolver) {
       BufferedConsole.write([], type, message, 4),
     ),
   );
+  const cacheFS = {[path]: testSource};
   setGlobal(env.global, 'console', testConsole);
-  const runtime = new ModuleLoader(config, env, resolver);
+  const runtime = new ModuleLoader(config, env, resolver, cacheFS);
   const start = Date.now();
   return TestRunner(config, env, runtime, path)
     .then((result: TestResult) => {
diff --git a/packages/jest-runtime/src/index.js b/packages/jest-runtime/src/index.js
index 1685e8edd3ec..6d724052869e 100644
--- a/packages/jest-runtime/src/index.js
+++ b/packages/jest-runtime/src/index.js
@@ -92,11 +92,17 @@ class Runtime {
   _unmockList: ?RegExp;
   _virtualMocks: BooleanObject;
 
-  constructor(config: Config, environment: Environment, resolver: Resolver) {
+  constructor(
+    config: Config,
+    environment: Environment,
+    resolver: Resolver,
+    cacheFS?: {[path: string]: string}
+  ) {
     this._moduleRegistry = Object.create(null);
     this._internalModuleRegistry = Object.create(null);
     this._mockRegistry = Object.create(null);
     this._sourceMapRegistry = Object.create(null);
+    this._cacheFS = cacheFS || Object.create(null);
     this._config = config;
     this._environment = environment;
     this._resolver = resolver;
@@ -455,9 +461,15 @@ class Runtime {
     localModule.paths = this._resolver.getModulePaths(dirname);
     localModule.require = this._createRequireImplementation(filename, options);
 
-    const transformedFile = transform(filename, this._config, {
-      isInternalModule,
-    });
+    const transformedFile = transform(
+      filename,
+      this._config,
+      {
+        isInternalModule,
+      },
+      this._cacheFS[filename]
+    );
+
 
     if (transformedFile.sourceMapPath) {
       this._sourceMapRegistry[filename] = transformedFile.sourceMapPath;
diff --git a/packages/jest-runtime/src/transform.js b/packages/jest-runtime/src/transform.js
index a3b063600576..8d141d56a543 100644
--- a/packages/jest-runtime/src/transform.js
+++ b/packages/jest-runtime/src/transform.js
@@ -346,9 +346,10 @@ const transformAndBuildScript = (
   config: Config,
   options: ?Options,
   instrument: boolean,
+  fileSource?: string
 ): BuiltTransformResult => {
   const isInternalModule = !!(options && options.isInternalModule);
-  const content = stripShebang(fs.readFileSync(filename, 'utf8'));
+  const content = stripShebang(fileSource || fs.readFileSync(filename, 'utf8'));
   let wrappedCode: string;
   let sourceMapPath: ?string = null;
   const willTransform = !isInternalModule &&
@@ -396,6 +397,7 @@ module.exports = (
   filename: Path,
   config: Config,
   options: Options,
+  fileSource?: string
 ): BuiltTransformResult => {
   const instrument = shouldInstrument(filename, config);
   const scriptCacheKey = getScriptCacheKey(filename, config, instrument);
@@ -403,7 +405,13 @@ module.exports = (
   if (result) {
     return result;
   } else {
-    result = transformAndBuildScript(filename, config, options, instrument);
+    result = transformAndBuildScript(
+      filename,
+      config,
+      options,
+      instrument,
+      fileSource
+    );
     cache.set(scriptCacheKey, result);
     return result;
   }