diff --git a/.flowconfig b/.flowconfig
index 9be0cd2..497f3b5 100644
--- a/.flowconfig
+++ b/.flowconfig
@@ -29,8 +29,8 @@ unsafe-getters-setters=error
 unnecessary-optional-chain=error
 unnecessary-invariant=error
 signature-verification-failure=error
-implicit-inexact-object=error
-ambiguous-object-type=error
+implicit-inexact-object=off
+ambiguous-object-type=off
 uninitialized-instance-property=error
 unsafe-addition=error
 
@@ -39,6 +39,7 @@ include_warnings=true
 module.use_strict=true
 babel_loose_array_spread=true
 esproposal.optional_chaining=enable
+exact_by_default=true
 
 [version]
 ^0.127.0
diff --git a/src/connection/arrayconnection.js b/src/connection/arrayconnection.js
index 8af688a..5aba906 100644
--- a/src/connection/arrayconnection.js
+++ b/src/connection/arrayconnection.js
@@ -8,10 +8,10 @@ import type {
   ConnectionCursor,
 } from './connectiontypes';
 
-type ArraySliceMetaInfo = {|
+type ArraySliceMetaInfo = {
   sliceStart: number,
   arrayLength: number,
-|};
+};
 
 /**
  * A simple function that accepts an array and connection arguments, and returns
diff --git a/src/connection/connection.js b/src/connection/connection.js
index d22ea9c..32b516c 100644
--- a/src/connection/connection.js
+++ b/src/connection/connection.js
@@ -51,19 +51,19 @@ export const connectionArgs: GraphQLFieldConfigArgumentMap = {
   ...backwardConnectionArgs,
 };
 
-type ConnectionConfig = {|
+type ConnectionConfig = {
   name?: ?string,
   nodeType: GraphQLObjectType,
   resolveNode?: ?GraphQLFieldResolver<any, any>,
   resolveCursor?: ?GraphQLFieldResolver<any, any>,
   edgeFields?: ?Thunk<GraphQLFieldConfigMap<any, any>>,
   connectionFields?: ?Thunk<GraphQLFieldConfigMap<any, any>>,
-|};
+};
 
-type GraphQLConnectionDefinitions = {|
+type GraphQLConnectionDefinitions = {
   edgeType: GraphQLObjectType,
   connectionType: GraphQLObjectType,
-|};
+};
 
 function resolveMaybeThunk<T>(thingOrThunk: Thunk<T>): T {
   return typeof thingOrThunk === 'function'
diff --git a/src/connection/connectiontypes.js b/src/connection/connectiontypes.js
index 5c10a70..6f2d09d 100644
--- a/src/connection/connectiontypes.js
+++ b/src/connection/connectiontypes.js
@@ -8,28 +8,28 @@ export type ConnectionCursor = string;
 /**
  * A flow type designed to be exposed as `PageInfo` over GraphQL.
  */
-export type PageInfo = {|
+export type PageInfo = {
   startCursor: ?ConnectionCursor,
   endCursor: ?ConnectionCursor,
   hasPreviousPage: ?boolean,
   hasNextPage: ?boolean,
-|};
+};
 
 /**
  * A flow type designed to be exposed as a `Connection` over GraphQL.
  */
-export type Connection<T> = {|
+export type Connection<T> = {
   edges: Array<Edge<T>>,
   pageInfo: PageInfo,
-|};
+};
 
 /**
  * A flow type designed to be exposed as a `Edge` over GraphQL.
  */
-export type Edge<T> = {|
+export type Edge<T> = {
   node: T,
   cursor: ConnectionCursor,
-|};
+};
 
 /**
  * A flow type describing the arguments a connection field receives in GraphQL.
diff --git a/src/mutation/mutation.js b/src/mutation/mutation.js
index 6fd59b1..0f39148 100644
--- a/src/mutation/mutation.js
+++ b/src/mutation/mutation.js
@@ -42,14 +42,14 @@ function resolveMaybeThunk<T>(thingOrThunk: Thunk<T>): T {
  * input field, and it should return an Object with a key for each
  * output field. It may return synchronously, or return a Promise.
  */
-type MutationConfig = {|
+type MutationConfig = {
   name: string,
   description?: string,
   deprecationReason?: string,
   inputFields: Thunk<GraphQLInputFieldConfigMap>,
   outputFields: Thunk<GraphQLFieldConfigMap<any, any>>,
   mutateAndGetPayload: MutationFn,
-|};
+};
 
 /**
  * Returns a GraphQLFieldConfig for the mutation described by the
diff --git a/src/node/node.js b/src/node/node.js
index ba54940..8dff2fd 100644
--- a/src/node/node.js
+++ b/src/node/node.js
@@ -15,11 +15,11 @@ import type {
 
 import { base64, unbase64 } from '../utils/base64';
 
-type GraphQLNodeDefinitions<TContext> = {|
+type GraphQLNodeDefinitions<TContext> = {
   nodeInterface: GraphQLInterfaceType,
   nodeField: GraphQLFieldConfig<mixed, TContext>,
   nodesField: GraphQLFieldConfig<mixed, TContext>,
-|};
+};
 
 /**
  * Given a function to map from an ID to an underlying object, and a function
@@ -77,10 +77,10 @@ export function nodeDefinitions<TContext>(
   return { nodeInterface, nodeField, nodesField };
 }
 
-type ResolvedGlobalId = {|
+type ResolvedGlobalId = {
   type: string,
   id: string,
-|};
+};
 
 /**
  * Takes a type name and an ID specific to that type name, and returns a
diff --git a/src/node/plural.js b/src/node/plural.js
index d992f50..b0623d7 100644
--- a/src/node/plural.js
+++ b/src/node/plural.js
@@ -9,7 +9,7 @@ import type {
   GraphQLResolveInfo,
 } from 'graphql';
 
-type PluralIdentifyingRootFieldConfig = {|
+type PluralIdentifyingRootFieldConfig = {
   argName: string,
   inputType: GraphQLInputType,
   outputType: GraphQLOutputType,
@@ -19,7 +19,7 @@ type PluralIdentifyingRootFieldConfig = {|
     info: GraphQLResolveInfo,
   ) => ?any,
   description?: ?string,
-|};
+};
 
 export function pluralIdentifyingRootField(
   config: PluralIdentifyingRootFieldConfig,