diff --git a/src/__tests__/starWarsData.js b/src/__tests__/starWarsData.js
index 1c2b848ed9..3b11e4febb 100644
--- a/src/__tests__/starWarsData.js
+++ b/src/__tests__/starWarsData.js
@@ -100,23 +100,23 @@ export type Character = {
   appearsIn: Array<number>,
 };
 
-export type Human = {
+export type Human = {|
   type: 'Human',
   id: string,
   name: string,
   friends: Array<string>,
   appearsIn: Array<number>,
   homePlanet: string,
-};
+|};
 
-export type Droid = {
+export type Droid = {|
   type: 'Droid',
   id: string,
   name: string,
   friends: Array<string>,
   appearsIn: Array<number>,
   primaryFunction: string,
-};
+|};
 
 /**
  * Helper function to get a character by ID.
diff --git a/src/execution/execute.js b/src/execution/execute.js
index ef962dce9e..77f95103d2 100644
--- a/src/execution/execute.js
+++ b/src/execution/execute.js
@@ -94,7 +94,7 @@ import type {
  * Namely, schema of the type system that is currently executing,
  * and the fragments defined in the query document
  */
-export type ExecutionContext = {
+export type ExecutionContext = {|
   schema: GraphQLSchema,
   fragments: ObjMap<FragmentDefinitionNode>,
   rootValue: mixed,
@@ -103,7 +103,7 @@ export type ExecutionContext = {
   variableValues: { [variable: string]: mixed },
   fieldResolver: GraphQLFieldResolver<any, any>,
   errors: Array<GraphQLError>,
-};
+|};
 
 /**
  * The result of GraphQL execution.
diff --git a/src/language/ast.js b/src/language/ast.js
index 21bc1797db..22169c327d 100644
--- a/src/language/ast.js
+++ b/src/language/ast.js
@@ -136,7 +136,7 @@ export type ASTNode =
 /**
  * Utility type listing all nodes indexed by their kind.
  */
-export type ASTKindToNode = {
+export type ASTKindToNode = {|
   Name: NameNode,
   Document: DocumentNode,
   OperationDefinition: OperationDefinitionNode,
@@ -180,7 +180,7 @@ export type ASTKindToNode = {
   UnionTypeExtension: UnionTypeExtensionNode,
   EnumTypeExtension: EnumTypeExtensionNode,
   InputObjectTypeExtension: InputObjectTypeExtensionNode,
-};
+|};
 
 // Name
 
diff --git a/src/language/source.js b/src/language/source.js
index 258249f38e..94a875fc52 100644
--- a/src/language/source.js
+++ b/src/language/source.js
@@ -10,10 +10,10 @@
 import invariant from '../jsutils/invariant';
 import defineToStringTag from '../jsutils/defineToStringTag';
 
-type Location = {
+type Location = {|
   line: number,
   column: number,
-};
+|};
 
 /**
  * A representation of source input to GraphQL.