diff --git a/packages/metro-bundler/src/Bundler/index.js b/packages/metro-bundler/src/Bundler/index.js
index 90d19952..a3c22002 100644
--- a/packages/metro-bundler/src/Bundler/index.js
+++ b/packages/metro-bundler/src/Bundler/index.js
@@ -251,12 +251,9 @@ class Bundler {
     return this._assetServer;
   }
 
-  end() {
+  async end() {
     this._transformer.kill();
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
-    return this._resolverPromise.then(resolver =>
+    await this._resolverPromise.then(resolver =>
       resolver
         .getDependencyGraph()
         .getWatcher()
@@ -353,7 +350,7 @@ class Bundler {
     });
   }
 
-  _bundle({
+  _bundle<T: Bundle | HMRBundle>({
     assetPlugins,
     bundle,
     dev,
@@ -372,7 +369,7 @@ class Bundler {
     unbundle,
   }: {
     assetPlugins?: Array<string>,
-    bundle: Bundle | HMRBundle,
+    bundle: T,
     dev: boolean,
     entryFile?: string,
     entryModuleOnly?: boolean,
@@ -387,7 +384,7 @@ class Bundler {
     runBeforeMainModule?: Array<string>,
     runModule?: boolean,
     unbundle?: boolean,
-  }) {
+  }): Promise<T> {
     const onResolutionResponse = (
       response: ResolutionResponse<Module, BundlingOptions>,
     ) => {
@@ -463,7 +460,7 @@ class Bundler {
     });
   }
 
-  _buildBundle({
+  _buildBundle<T: Bundle | HMRBundle>({
     entryFile,
     dev,
     minify,
@@ -479,7 +476,7 @@ class Bundler {
     onModuleTransformed = emptyFunction,
     finalizeBundle = emptyFunction,
     onProgress = emptyFunction,
-  }: *) {
+  }: *): Promise<T> {
     const transformingFilesLogEntry = log(
       createActionStartEntry({
         action_name: 'Transforming files',
@@ -505,9 +502,6 @@ class Bundler {
       });
     }
 
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
     return Promise.all([
       this._resolverPromise,
       resolutionResponse,
@@ -683,10 +677,7 @@ class Bundler {
     +platform: string,
     +minify: boolean,
     +generateSourceMaps: boolean,
-  }) {
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
+  }): Promise<Array<string>> {
     return this.getDependencies({
       entryFile,
       rootEntryFile: entryFile,
@@ -698,7 +689,8 @@ class Bundler {
     }).then(({dependencies}) => {
       const ret = [];
       const promises = [];
-      const placeHolder = {};
+      /* $FlowFixMe: these are always removed */
+      const placeHolder: string = {};
       dependencies.forEach(dep => {
         if (dep.isAsset()) {
           const localPath = toLocalPath(this._projectRoots, dep.path);
diff --git a/packages/metro-bundler/src/Bundler/util.js b/packages/metro-bundler/src/Bundler/util.js
index 0328933a..b1039e17 100644
--- a/packages/metro-bundler/src/Bundler/util.js
+++ b/packages/metro-bundler/src/Bundler/util.js
@@ -256,11 +256,8 @@ function* filter(iterator, predicate) {
   }
 }
 
-/* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an error
- * found when Flow v0.54 was deployed. To see the error delete this comment and
- * run Flow. */
-class ArrayMap extends Map {
-  get(key) {
+class ArrayMap<K, V> extends Map<K, Array<V>> {
+  get(key: K): Array<V> {
     let array = super.get(key);
     if (!array) {
       array = [];
diff --git a/packages/metro-bundler/src/Config.js b/packages/metro-bundler/src/Config.js
index 5dd94834..e5d6f29b 100644
--- a/packages/metro-bundler/src/Config.js
+++ b/packages/metro-bundler/src/Config.js
@@ -138,11 +138,8 @@ export type ConfigT = {
   runBeforeMainModule: Array<string>,
 };
 
-/* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an error
- * found when Flow v0.56 was deployed. To see the error delete this comment and
- * run Flow. */
 const DEFAULT = ({
-  extraNodeModules: Object.create(null),
+  extraNodeModules: {},
   getAssetExts: () => [],
   getBlacklistRE: () => blacklist(),
   getEnableBabelRCLookup: () => false,
diff --git a/packages/metro-bundler/src/DeltaBundler/DeltaTransformer.js b/packages/metro-bundler/src/DeltaBundler/DeltaTransformer.js
index f135302a..f3d55df5 100644
--- a/packages/metro-bundler/src/DeltaBundler/DeltaTransformer.js
+++ b/packages/metro-bundler/src/DeltaBundler/DeltaTransformer.js
@@ -50,7 +50,10 @@ export type DeltaTransformResponse = {|
   +pre: DeltaEntries,
   +post: DeltaEntries,
   +delta: DeltaEntries,
-  +inverseDependencies: {[key: string]: $ReadOnlyArray<string>},
+  +inverseDependencies: {
+    [key: string]: $ReadOnlyArray<string>,
+    __proto__: null,
+  },
   +reset: boolean,
 |};
 
@@ -317,7 +320,7 @@ class DeltaTransformer extends EventEmitter {
    */
   _getInverseDependencies(
     dependencyEdges: DependencyEdges,
-  ): {[key: string]: $ReadOnlyArray<string>} {
+  ): {[key: string]: $ReadOnlyArray<string>, __proto__: null} {
     const output = Object.create(null);
 
     for (const [path, {inverseDependencies}] of dependencyEdges.entries()) {
@@ -326,9 +329,6 @@ class DeltaTransformer extends EventEmitter {
       ).map(dep => this._getModuleId({path: dep}));
     }
 
-    /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.56 was deployed. To see the error delete this
-     * comment and run Flow. */
     return output;
   }
 
diff --git a/packages/metro-bundler/src/JSTransformer/index.js b/packages/metro-bundler/src/JSTransformer/index.js
index 8ea19988..00128764 100644
--- a/packages/metro-bundler/src/JSTransformer/index.js
+++ b/packages/metro-bundler/src/JSTransformer/index.js
@@ -21,7 +21,11 @@ const path = require('path');
 const util = require('util');
 const workerFarm = require('../worker-farm');
 
-import type {Data as TransformData, Options as WorkerOptions} from './worker';
+import type {
+  Data as TransformData,
+  Options as WorkerOptions,
+  TransformedCode,
+} from './worker';
 import type {LocalPath} from '../node-haste/lib/toLocalPath';
 import type {MappingsMap} from '../lib/SourceMap';
 import typeof {
@@ -142,10 +146,7 @@ class Transformer {
 
   kill() {
     if (this._usesFarm && this._workers) {
-      /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an
-       * error found when Flow v0.56 was deployed. To see the error delete this
-       * comment and run Flow. */
-      workerFarm.end(this._workers);
+      workerFarm.end(this._workers, () => {});
     }
   }
 
@@ -154,17 +155,12 @@ class Transformer {
     localPath: LocalPath,
     code: string,
     options: WorkerOptions,
-  ) {
+  ): Promise<TransformedCode> {
     if (!this._transform) {
-      /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-       * error found when Flow v0.54 was deployed. To see the error delete this
-       * comment and run Flow. */
       return Promise.reject(new Error('No transform module'));
     }
     debug('transforming file', fileName);
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
+
     return this._transform(
       this._transformModulePath,
       fileName,
diff --git a/packages/metro-bundler/src/Resolver/polyfills/require.js b/packages/metro-bundler/src/Resolver/polyfills/require.js
index b6b2e8b1..164190e4 100644
--- a/packages/metro-bundler/src/Resolver/polyfills/require.js
+++ b/packages/metro-bundler/src/Resolver/polyfills/require.js
@@ -46,22 +46,19 @@ type ModuleDefinition = {|
   isInitialized: boolean,
   verboseName?: string,
 |};
-type ModuleMap = {[key: ModuleID]: ModuleDefinition};
+type ModuleMap = {[key: ModuleID]: ModuleDefinition, __proto__: null};
 type RequireFn = (id: ModuleID | VerboseModuleNameForDev) => Exports;
 type VerboseModuleNameForDev = string;
 
 global.require = require;
 global.__d = define;
 
-/* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an error
- * found when Flow v0.56 was deployed. To see the error delete this comment and
- * run Flow. */
 const modules: ModuleMap = Object.create(null);
 if (__DEV__) {
-  /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an error
-   * found when Flow v0.56 was deployed. To see the error delete this comment
-   * and run Flow. */
-  var verboseNamesToModuleIds: {[key: string]: number} = Object.create(null);
+  var verboseNamesToModuleIds: {
+    [key: string]: number,
+    __proto__: null,
+  } = Object.create(null);
 }
 
 function define(
diff --git a/packages/metro-bundler/src/Server/index.js b/packages/metro-bundler/src/Server/index.js
index 7d4437a3..8622288a 100644
--- a/packages/metro-bundler/src/Server/index.js
+++ b/packages/metro-bundler/src/Server/index.js
@@ -24,6 +24,7 @@ const formatBundlingError = require('../lib/formatBundlingError');
 const getMaxWorkers = require('../lib/getMaxWorkers');
 const getOrderedDependencyPaths = require('../lib/getOrderedDependencyPaths');
 const mime = require('mime-types');
+const nullthrows = require('fbjs/lib/nullthrows');
 const parsePlatformFilePath = require('../node-haste/lib/parsePlatformFilePath');
 const path = require('path');
 const symbolicate = require('./symbolicate');
@@ -175,7 +176,7 @@ class Server {
     workerPath: ?string,
   };
   _projectRoots: $ReadOnlyArray<string>;
-  _bundles: {};
+  _bundles: {__proto__: null};
   _bundleBuildInfos: WeakMap<Bundle, BuildInfo>;
   _changeWatchers: Array<{
     req: IncomingMessage,
@@ -237,9 +238,6 @@ class Server {
 
     this._reporter = reporter;
     this._projectRoots = this._opts.projectRoots;
-    /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.56 was deployed. To see the error delete this
-     * comment and run Flow. */
     this._bundles = Object.create(null);
     this._bundleBuildInfos = new WeakMap();
     this._changeWatchers = [];
@@ -275,11 +273,9 @@ class Server {
         for (const key in this._bundles) {
           this._bundles[key]
             .then(bundle => {
-              const deps = bundleDeps.get(bundle);
+              const deps = nullthrows(bundleDeps.get(bundle));
               filePaths.forEach(filePath => {
-                // $FlowFixMe(>=0.37.0)
                 if (deps.files.has(filePath)) {
-                  // $FlowFixMe(>=0.37.0)
                   deps.outdated.add(filePath);
                 }
               });
@@ -506,9 +502,6 @@ class Server {
   }
 
   _clearBundles() {
-    /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.56 was deployed. To see the error delete this
-     * comment and run Flow. */
     this._bundles = Object.create(null);
   }
 
@@ -700,8 +693,7 @@ class Server {
 
     if (optionsJson in this._bundles) {
       return this._bundles[optionsJson].then(bundle => {
-        const deps = bundleDeps.get(bundle);
-        // $FlowFixMe(>=0.37.0)
+        const deps = nullthrows(bundleDeps.get(bundle));
         const {dependencyPairs, files, idToIndex, outdated} = deps;
         if (outdated.size) {
           const updatingExistingBundleLogEntry = log(
@@ -713,7 +705,6 @@ class Server {
 
           debug('Attempt to update existing bundle');
 
-          // $FlowFixMe(>=0.37.0)
           deps.outdated = new Set();
 
           const {platform, dev, minify, hot} = options;
diff --git a/packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionRequest.js b/packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionRequest.js
index f41fe2a7..98ae408a 100644
--- a/packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionRequest.js
+++ b/packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionRequest.js
@@ -68,7 +68,7 @@ type Options<TModule, TPackage> = {|
 |};
 
 class ResolutionRequest<TModule: Moduleish, TPackage: Packageish> {
-  _immediateResolutionCache: {[key: string]: TModule};
+  _immediateResolutionCache: {[key: string]: TModule, __proto__: null};
   _options: Options<TModule, TPackage>;
   static AmbiguousModuleResolutionError: Class<AmbiguousModuleResolutionError>;
 
@@ -146,7 +146,7 @@ class ResolutionRequest<TModule: Moduleish, TPackage: Packageish> {
     transformOptions: TransformWorkerOptions,
     onProgress?: ?(finishedModules: number, totalModules: number) => mixed,
     recursive: boolean,
-  }) {
+  }): Promise<void> {
     const entry = this._options.moduleCache.getModule(this._options.entryPath);
 
     response.pushDependency(entry);
@@ -245,9 +245,6 @@ class ResolutionRequest<TModule: Moduleish, TPackage: Packageish> {
       return promise.then(value => [key, value]);
     }
 
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
     return Promise.all([
       // kicks off recursive dependency discovery, but doesn't block until it's
       // done
@@ -363,13 +360,10 @@ class ResolutionRequest<TModule: Moduleish, TPackage: Packageish> {
   }
 
   _resetResolutionCache() {
-    /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.56 was deployed. To see the error delete this
-     * comment and run Flow. */
     this._immediateResolutionCache = Object.create(null);
   }
 
-  getResolutionCache(): {[key: string]: TModule} {
+  getResolutionCache(): {[key: string]: TModule, __proto__: null} {
     return this._immediateResolutionCache;
   }
 }
diff --git a/packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionResponse.js b/packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionResponse.js
index 590e7737..e136ce59 100644
--- a/packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionResponse.js
+++ b/packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionResponse.js
@@ -24,7 +24,7 @@ class ResolutionResponse<TModule: {hash(): string}, TOptions> {
   // This is monkey-patched from Resolver.
   getModuleId: ?() => number;
 
-  _mappings: {[hash: string]: Array<[string, TModule]>};
+  _mappings: {[hash: string]: Array<[string, TModule]>, __proto__: null};
   _finalized: boolean;
   _mainModule: ?TModule;
 
@@ -34,9 +34,6 @@ class ResolutionResponse<TModule: {hash(): string}, TOptions> {
     this.mocks = null;
     this.numPrependedDependencies = 0;
     this.options = options;
-    /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.56 was deployed. To see the error delete this
-     * comment and run Flow. */
     this._mappings = Object.create(null);
     this._finalized = false;
   }
diff --git a/packages/metro-bundler/src/node-haste/Module.js b/packages/metro-bundler/src/node-haste/Module.js
index 5a772d3b..21f7909f 100644
--- a/packages/metro-bundler/src/node-haste/Module.js
+++ b/packages/metro-bundler/src/node-haste/Module.js
@@ -144,18 +144,12 @@ class Module {
     return this._getHasteName() != null;
   }
 
-  getCode(transformOptions: WorkerOptions) {
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
-    return this.read(transformOptions).then(({code}) => code);
+  async getCode(transformOptions: WorkerOptions): Promise<string> {
+    return (await this.read(transformOptions)).code;
   }
 
-  getMap(transformOptions: WorkerOptions) {
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
-    return this.read(transformOptions).then(({map}) => map);
+  async getMap(transformOptions: WorkerOptions) {
+    return (await this.read(transformOptions)).map;
   }
 
   getName(): string {
@@ -186,11 +180,8 @@ class Module {
     return this._moduleCache.getPackageForModule(this);
   }
 
-  getDependencies(transformOptions: WorkerOptions) {
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
-    return this.read(transformOptions).then(({dependencies}) => dependencies);
+  async getDependencies(transformOptions: WorkerOptions) {
+    return (await this.read(transformOptions)).dependencies;
   }
 
   /**
diff --git a/packages/metro-bundler/src/node-haste/ModuleCache.js b/packages/metro-bundler/src/node-haste/ModuleCache.js
index b8bd5002..903e2573 100644
--- a/packages/metro-bundler/src/node-haste/ModuleCache.js
+++ b/packages/metro-bundler/src/node-haste/ModuleCache.js
@@ -33,9 +33,9 @@ class ModuleCache {
   _getClosestPackage: GetClosestPackageFn;
   _getTransformCacheKey: GetTransformCacheKey;
   _globalTransformCache: ?GlobalTransformCache;
-  _moduleCache: {[filePath: string]: Module};
+  _moduleCache: {[filePath: string]: Module, __proto__: null};
   _moduleOptions: ModuleOptions;
-  _packageCache: {[filePath: string]: Package};
+  _packageCache: {[filePath: string]: Package, __proto__: null};
   _packageModuleMap: WeakMap<Module, string>;
   _platforms: Set<string>;
   _transformCode: TransformCode;
@@ -72,14 +72,8 @@ class ModuleCache {
     this._getTransformCacheKey = getTransformCacheKey;
     this._globalTransformCache = globalTransformCache;
     this._depGraphHelpers = depGraphHelpers;
-    /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.56 was deployed. To see the error delete this
-     * comment and run Flow. */
     this._moduleCache = Object.create(null);
     this._moduleOptions = moduleOptions;
-    /* $FlowFixMe(>=0.56.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.56 was deployed. To see the error delete this
-     * comment and run Flow. */
     this._packageCache = Object.create(null);
     this._packageModuleMap = new WeakMap();
     this._platforms = platforms;
@@ -144,9 +138,8 @@ class ModuleCache {
   }
 
   getPackageForModule(module: Module): ?Package {
-    if (this._packageModuleMap.has(module)) {
-      const packagePath = this._packageModuleMap.get(module);
-      // $FlowFixMe(>=0.37.0)
+    let packagePath = this._packageModuleMap.get(module);
+    if (packagePath) {
       if (this._packageCache[packagePath]) {
         return this._packageCache[packagePath];
       } else {
@@ -154,7 +147,7 @@ class ModuleCache {
       }
     }
 
-    const packagePath = this._getClosestPackage(module.path);
+    packagePath = this._getClosestPackage(module.path);
     if (!packagePath) {
       return null;
     }
diff --git a/packages/metro-bundler/src/node-haste/Polyfill.js b/packages/metro-bundler/src/node-haste/Polyfill.js
index b4f68281..84ec03be 100644
--- a/packages/metro-bundler/src/node-haste/Polyfill.js
+++ b/packages/metro-bundler/src/node-haste/Polyfill.js
@@ -43,11 +43,8 @@ class Polyfill extends Module {
     return null;
   }
 
-  getDependencies() {
-    /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
-    return Promise.resolve(this._dependencies);
+  async getDependencies() {
+    return this._dependencies;
   }
 
   isJSON() {
diff --git a/packages/metro-bundler/src/shared/output/unbundle/as-indexed-file.js b/packages/metro-bundler/src/shared/output/unbundle/as-indexed-file.js
index 2aba0314..bf500dd3 100644
--- a/packages/metro-bundler/src/shared/output/unbundle/as-indexed-file.js
+++ b/packages/metro-bundler/src/shared/output/unbundle/as-indexed-file.js
@@ -40,10 +40,7 @@ function saveAsIndexedFile(
   bundle: RamBundleInfo,
   options: OutputOptions,
   log: (...args: Array<string>) => void,
-  /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an error
- * found when Flow v0.54 was deployed. To see the error delete this comment and
- * run Flow. */
-): Promise<> {
+): Promise<mixed> {
   const {
     bundleOutput,
     bundleEncoding: encoding,
diff --git a/packages/metro-bundler/src/shared/output/unbundle/index.js b/packages/metro-bundler/src/shared/output/unbundle/index.js
index c53f90fa..f7304dfb 100644
--- a/packages/metro-bundler/src/shared/output/unbundle/index.js
+++ b/packages/metro-bundler/src/shared/output/unbundle/index.js
@@ -43,10 +43,7 @@ function saveUnbundle(
   // overhead when reading hundreds pf assets from disk
   return options.platform === 'android' && !options.indexedUnbundle
     ? asAssets(bundle, options, log)
-    : /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an
-     * error found when Flow v0.54 was deployed. To see the error delete this
-     * comment and run Flow. */
-      asIndexedFile(bundle, options, log);
+    : asIndexedFile(bundle, options, log);
 }
 
 exports.build = buildBundle;
diff --git a/packages/metro-bundler/src/shared/output/unbundle/write-sourcemap.js b/packages/metro-bundler/src/shared/output/unbundle/write-sourcemap.js
index 7d828d8a..c0c2af4d 100644
--- a/packages/metro-bundler/src/shared/output/unbundle/write-sourcemap.js
+++ b/packages/metro-bundler/src/shared/output/unbundle/write-sourcemap.js
@@ -17,10 +17,7 @@ function writeSourcemap(
   fileName: string,
   contents: string,
   log: (...args: Array<string>) => void,
-  /* $FlowFixMe(>=0.54.0 site=react_native_fb) This comment suppresses an error
- * found when Flow v0.54 was deployed. To see the error delete this comment and
- * run Flow. */
-): Promise<> {
+): Promise<mixed> {
   if (!fileName) {
     return Promise.resolve();
   }