diff --git a/src/isomorphic/classic/element/ReactElementType.js b/src/isomorphic/classic/element/ReactElementType.js
index e959241737..9702b0f77a 100644
--- a/src/isomorphic/classic/element/ReactElementType.js
+++ b/src/isomorphic/classic/element/ReactElementType.js
@@ -29,7 +29,7 @@ export type ReactElement = {
 
   // __DEV__
   _store: {
-    validated: bool,
+    validated: boolean,
   },
   _self: ReactElement,
   _shadowChildren: any,
diff --git a/src/isomorphic/hooks/ReactComponentTreeHook.js b/src/isomorphic/hooks/ReactComponentTreeHook.js
index 929ed7c98f..ae769001c9 100644
--- a/src/isomorphic/hooks/ReactComponentTreeHook.js
+++ b/src/isomorphic/hooks/ReactComponentTreeHook.js
@@ -297,7 +297,7 @@ var ReactComponentTreeHook = {
     unmountedIDs.length = 0;
   },
 
-  isMounted(id: DebugID): bool {
+  isMounted(id: DebugID): boolean {
     var item = getItem(id);
     return item ? item.isMounted : false;
   },
diff --git a/src/renderers/native/ReactNativeTagHandles.js b/src/renderers/native/ReactNativeTagHandles.js
index 2a4d7bd010..d0c7bb2685 100644
--- a/src/renderers/native/ReactNativeTagHandles.js
+++ b/src/renderers/native/ReactNativeTagHandles.js
@@ -48,7 +48,7 @@ var ReactNativeTagHandles = {
     );
   },
 
-  reactTagIsNativeTopRootID: function(reactTag: number): bool {
+  reactTagIsNativeTopRootID: function(reactTag: number): boolean {
     // We reserve all tags that are 1 mod 10 for native root views
     return reactTag % 10 === 1;
   },
diff --git a/src/renderers/native/__mocks__/deepDiffer.js b/src/renderers/native/__mocks__/deepDiffer.js
index cc58e4b328..34e4da74a0 100644
--- a/src/renderers/native/__mocks__/deepDiffer.js
+++ b/src/renderers/native/__mocks__/deepDiffer.js
@@ -11,7 +11,7 @@
 
 // TODO: Move deepDiffer into react
 
-var deepDiffer = function(one: any, two: any): bool {
+var deepDiffer = function(one: any, two: any): boolean {
   if (one === two) {
     // Short circuit on identical object references instead of traversing them.
     return false;
diff --git a/src/renderers/shared/ReactDebugTool.js b/src/renderers/shared/ReactDebugTool.js
index 7b726d7dd1..31ef8c7073 100644
--- a/src/renderers/shared/ReactDebugTool.js
+++ b/src/renderers/shared/ReactDebugTool.js
@@ -254,7 +254,7 @@ function resumeCurrentLifeCycleTimer() {
 }
 
 var lastMarkTimeStamp = 0;
-var canUsePerformanceMeasure: bool =
+var canUsePerformanceMeasure: boolean =
 // $FlowFixMe https://github.com/facebook/flow/issues/2345
   typeof performance !== 'undefined' &&
   typeof performance.mark === 'function' &&
@@ -323,7 +323,7 @@ var ReactDebugTool = {
       }
     }
   },
-  isProfiling(): bool {
+  isProfiling(): boolean {
     return isProfiling;
   },
   beginProfiling(): void {
diff --git a/src/renderers/shared/fiber/ReactFiberReconciler.js b/src/renderers/shared/fiber/ReactFiberReconciler.js
index 4ece60a0f2..d5e03669e6 100644
--- a/src/renderers/shared/fiber/ReactFiberReconciler.js
+++ b/src/renderers/shared/fiber/ReactFiberReconciler.js
@@ -40,7 +40,7 @@ export type HostConfig<T, P, I, C> = {
   updateContainer(containerInfo : C, children : HostChildren<I>) : void;
 
   createInstance(type : T, props : P, children : HostChildren<I>) : I,
-  prepareUpdate(instance : I, oldProps : P, newProps : P, children : HostChildren<I>) : bool,
+  prepareUpdate(instance : I, oldProps : P, newProps : P, children : HostChildren<I>) : boolean,
   commitUpdate(instance : I, oldProps : P, newProps : P, children : HostChildren<I>) : void,
   deleteInstance(instance : I) : void,
 
diff --git a/src/renderers/shared/fiber/ReactFiberRoot.js b/src/renderers/shared/fiber/ReactFiberRoot.js
index c0b312253c..1c972700b0 100644
--- a/src/renderers/shared/fiber/ReactFiberRoot.js
+++ b/src/renderers/shared/fiber/ReactFiberRoot.js
@@ -22,7 +22,7 @@ export type FiberRoot = {
   // The currently active root fiber. This is the mutable root of the tree.
   current: Fiber,
   // Determines if this root has already been added to the schedule for work.
-  isScheduled: bool,
+  isScheduled: boolean,
   // The work schedule is a linked list.
   nextScheduledRoot: ?FiberRoot,
 };
diff --git a/src/renderers/shared/stack/reconciler/ReactInstanceType.js b/src/renderers/shared/stack/reconciler/ReactInstanceType.js
index d647f4afc9..15f321b6cb 100644
--- a/src/renderers/shared/stack/reconciler/ReactInstanceType.js
+++ b/src/renderers/shared/stack/reconciler/ReactInstanceType.js
@@ -34,5 +34,5 @@ export type ReactInstance = {
   _mountImage: any,
   // __DEV__
   _debugID: DebugID,
-  _warnedAboutRefsInRender: bool,
+  _warnedAboutRefsInRender: boolean,
 };
diff --git a/src/renderers/shared/stack/reconciler/ReactOwner.js b/src/renderers/shared/stack/reconciler/ReactOwner.js
index 270f7fb933..c634dfb384 100644
--- a/src/renderers/shared/stack/reconciler/ReactOwner.js
+++ b/src/renderers/shared/stack/reconciler/ReactOwner.js
@@ -21,7 +21,7 @@ import type { ReactInstance } from 'ReactInstanceType';
  * @return {boolean} True if `object` is a valid owner.
  * @final
  */
-function isValidOwner(object: any): bool {
+function isValidOwner(object: any): boolean {
   return !!(
     object &&
     typeof object.attachRef === 'function' &&
diff --git a/src/renderers/shared/stack/reconciler/ReactRef.js b/src/renderers/shared/stack/reconciler/ReactRef.js
index 43210a5a26..4781561b91 100644
--- a/src/renderers/shared/stack/reconciler/ReactRef.js
+++ b/src/renderers/shared/stack/reconciler/ReactRef.js
@@ -53,7 +53,7 @@ ReactRef.attachRefs = function(
 ReactRef.shouldUpdateRefs = function(
   prevElement: ReactElement | string | number | null | false,
   nextElement: ReactElement | string | number | null | false,
-): bool {
+): boolean {
   // If either the owner or a `ref` has changed, make sure the newest owner
   // has stored a reference to `this`, and the previous owner (if different)
   // has forgotten the reference to `this`. We use the element instead
diff --git a/src/renderers/shared/utils/Transaction.js b/src/renderers/shared/utils/Transaction.js
index b8bee0b169..afa8bc9b38 100644
--- a/src/renderers/shared/utils/Transaction.js
+++ b/src/renderers/shared/utils/Transaction.js
@@ -103,7 +103,7 @@ var TransactionImpl = {
    */
   getTransactionWrappers: null,
 
-  isInTransaction: function(): bool {
+  isInTransaction: function(): boolean {
     return !!this._isInTransaction;
   },
 
diff --git a/src/renderers/shared/utils/isTextInputElement.js b/src/renderers/shared/utils/isTextInputElement.js
index c2635ac5e2..e464daae31 100644
--- a/src/renderers/shared/utils/isTextInputElement.js
+++ b/src/renderers/shared/utils/isTextInputElement.js
@@ -33,7 +33,7 @@ var supportedInputTypes: {[key: string]: true | void} = {
   'week': true,
 };
 
-function isTextInputElement(elem: ?HTMLElement): bool {
+function isTextInputElement(elem: ?HTMLElement): boolean {
   var nodeName = elem && elem.nodeName && elem.nodeName.toLowerCase();
 
   if (nodeName === 'input') {