diff --git a/react-packager/src/Bundler/BundleBase.js b/react-packager/src/Bundler/BundleBase.js
index 4d2ce0d2..35c8a56d 100644
--- a/react-packager/src/Bundler/BundleBase.js
+++ b/react-packager/src/Bundler/BundleBase.js
@@ -110,7 +110,11 @@ class BundleBase {
 
   setRamGroups(ramGroups: Array<string>) {}
 
-  toJSON(): mixed {
+  toJSON(): {
+    modules: Array<ModuleTransport>,
+    assets: Array<mixed>,
+    mainModuleId: number | void,
+  } {
     return {
       modules: this._modules,
       assets: this._assets,
diff --git a/react-packager/src/node-haste/Module.js b/react-packager/src/node-haste/Module.js
index ee5c28fc..3cea23d0 100644
--- a/react-packager/src/node-haste/Module.js
+++ b/react-packager/src/node-haste/Module.js
@@ -114,11 +114,11 @@ class Module {
     );
   }
 
-  getCode(transformOptions: mixed) {
+  getCode(transformOptions: Object) {
     return this.read(transformOptions).then(({code}) => code);
   }
 
-  getMap(transformOptions: mixed) {
+  getMap(transformOptions: Object) {
     return this.read(transformOptions).then(({map}) => map);
   }
 
@@ -154,7 +154,7 @@ class Module {
     return this._moduleCache.getPackageForModule(this);
   }
 
-  getDependencies(transformOptions: mixed) {
+  getDependencies(transformOptions: Object) {
     return this.read(transformOptions).then(({dependencies}) => dependencies);
   }
 
@@ -244,7 +244,7 @@ class Module {
    * dependencies, etc. The overall process is to read the cache first, and if
    * it's a miss, we let the worker write to the cache and read it again.
    */
-  read(transformOptions: mixed): Promise<ReadResult> {
+  read(transformOptions: Object): Promise<ReadResult> {
     const key = stableObjectHash(transformOptions || {});
     const promise = this._readPromises.get(key);
     if (promise != null) {
diff --git a/react-packager/src/node-haste/Package.js b/react-packager/src/node-haste/Package.js
index 3e4ffa1d..1961f273 100644
--- a/react-packager/src/node-haste/Package.js
+++ b/react-packager/src/node-haste/Package.js
@@ -165,6 +165,7 @@ function getReplacements(pkg) {
 
   // merge with "browser" as default,
   // "react-native" as override
+  // $FlowFixMe(>=0.35.0) browser and rn should be objects
   return { ...browser, ...rn };
 }