diff --git a/packager/src/Bundler/__tests__/Bundler-test.js b/packager/src/Bundler/__tests__/Bundler-test.js
index 981fd0233..939a8e4c5 100644
--- a/packager/src/Bundler/__tests__/Bundler-test.js
+++ b/packager/src/Bundler/__tests__/Bundler-test.js
@@ -171,7 +171,7 @@ describe('Bundler', function() {
               hot: false,
               inlineRequires: false,
               platform: undefined,
-              projectRoots,
+              projectRoot: projectRoots[0],
             },
           },
         },
diff --git a/packager/src/Bundler/index.js b/packager/src/Bundler/index.js
index 7094c5ff3..1715c00fe 100644
--- a/packager/src/Bundler/index.js
+++ b/packager/src/Bundler/index.js
@@ -821,7 +821,7 @@ class Bundler {
           hot,
           inlineRequires: extraOptions.inlineRequires || false,
           platform,
-          projectRoots: options.projectRoots,
+          projectRoot: options.projectRoots[0],
         }
       },
       preloadedModules: extraOptions.preloadedModules,
diff --git a/packager/src/JSTransformer/worker/worker.js b/packager/src/JSTransformer/worker/worker.js
index 335ab5a78..a3e978206 100644
--- a/packager/src/JSTransformer/worker/worker.js
+++ b/packager/src/JSTransformer/worker/worker.js
@@ -41,7 +41,7 @@ export type TransformOptions = {|
   +hot: boolean,
   +inlineRequires: {+blacklist: {[string]: true}} | boolean,
   +platform: string,
-  +projectRoots: Array<string>,
+  +projectRoot: string,
 |};
 
 export type Options = {|
diff --git a/packager/src/lib/GlobalTransformCache.js b/packager/src/lib/GlobalTransformCache.js
index df2cbe147..12deb44f8 100644
--- a/packager/src/lib/GlobalTransformCache.js
+++ b/packager/src/lib/GlobalTransformCache.js
@@ -383,7 +383,7 @@ class OptionsHasher {
    */
   hashTransformOptions(hash: crypto$Hash, options: TransformOptions): crypto$Hash {
     const {
-      generateSourceMaps, dev, hot, inlineRequires, platform, projectRoots,
+      generateSourceMaps, dev, hot, inlineRequires, platform, projectRoot,
       ...unknowns,
     } = options;
     const unknownKeys = Object.keys(unknowns);
@@ -401,14 +401,17 @@ class OptionsHasher {
     if (typeof inlineRequires === 'object') {
       relativeBlacklist = this.relativizeFilePaths(Object.keys(inlineRequires.blacklist));
     }
-    const relativeProjectRoots = this.relativizeFilePaths(projectRoots);
-    const optionTuple = [relativeBlacklist, relativeProjectRoots];
+    const relativeProjectRoot = this.relativizeFilePath(projectRoot);
+    const optionTuple = [relativeBlacklist, relativeProjectRoot];
     hash.update(JSON.stringify(optionTuple));
     return hash;
   }
 
   relativizeFilePaths(filePaths: Array<string>): Array<string> {
-    return filePaths.map(filepath => path.relative(this._rootPath, filepath));
+    return filePaths.map(this.relativizeFilePath);
+  }
+  relativizeFilePath(filePath: string): string {
+    return path.relative(this._rootPath, filePath);
   }
 }
 
diff --git a/packager/src/lib/__tests__/GlobalTransformCache-test.js b/packager/src/lib/__tests__/GlobalTransformCache-test.js
index 06b08e658..1b1bd7e9f 100644
--- a/packager/src/lib/__tests__/GlobalTransformCache-test.js
+++ b/packager/src/lib/__tests__/GlobalTransformCache-test.js
@@ -51,7 +51,7 @@ describe('GlobalTransformCache', () => {
         hot: false,
         inlineRequires: false,
         platform: 'ios',
-        projectRoots: [path.join(__dirname, 'root')],
+        projectRoot: path.join(__dirname, 'root'),
       },
     };
     const result = await Promise.all([cache.fetch({
diff --git a/packager/src/lib/__tests__/__snapshots__/GlobalTransformCache-test.js.snap b/packager/src/lib/__tests__/__snapshots__/GlobalTransformCache-test.js.snap
index 97bc9d3be..8c15dc7cd 100644
--- a/packager/src/lib/__tests__/__snapshots__/GlobalTransformCache-test.js.snap
+++ b/packager/src/lib/__tests__/__snapshots__/GlobalTransformCache-test.js.snap
@@ -19,12 +19,12 @@ Object {
 exports[`GlobalTransformCache fetches results 1`] = `
 Array [
   Object {
-    "code": "/* code from http://globalcache.com/57c9f999b0df46812db2a6bea665f5feb9d448ff-foo.js */",
+    "code": "/* code from http://globalcache.com/cd6df9b7e86839dafc5e9b5b493a28cbc55074e7-foo.js */",
     "dependencies": Array [],
     "dependencyOffsets": Array [],
   },
   Object {
-    "code": "/* code from http://globalcache.com/df53b0670d117d6b35ce58ff64d09909ece46a09-bar.js */",
+    "code": "/* code from http://globalcache.com/6329a317fcf94d74cc9a1de6442ee7c25e27a507-bar.js */",
     "dependencies": Array [],
     "dependencyOffsets": Array [],
   },
diff --git a/packager/transformer.js b/packager/transformer.js
index 88e22d52d..76e52dc48 100644
--- a/packager/transformer.js
+++ b/packager/transformer.js
@@ -30,19 +30,19 @@ const {compactMapping} = require('./src/Bundler/source-map');
 const getBabelRC = (function() {
   let babelRC = null;
 
-  return function _getBabelRC(projectRoots) {
+  return function _getBabelRC(projectRoot) {
     if (babelRC !== null) {
       return babelRC;
     }
 
     babelRC = {plugins: []}; // empty babelrc
 
-    // Let's look for the .babelrc in the first project root.
+    // Let's look for the .babelrc in the project root.
     // In the future let's look into adding a command line option to specify
     // this location.
     let projectBabelRCPath;
-    if (projectRoots && projectRoots.length > 0) {
-      projectBabelRCPath = path.resolve(projectRoots[0], '.babelrc');
+    if (projectRoot) {
+      projectBabelRCPath = path.resolve(projectRoot, '.babelrc');
     }
 
     // If a .babelrc file doesn't exist in the project,
@@ -70,7 +70,7 @@ const getBabelRC = (function() {
  * config object with the appropriate plugins.
  */
 function buildBabelConfig(filename, options) {
-  const babelRC = getBabelRC(options.projectRoots);
+  const babelRC = getBabelRC(options.projectRoot);
 
   const extraConfig = {
     code: false,