diff --git a/src/index.d.ts b/src/index.d.ts
index 1b518ee268..e408ae67cb 100644
--- a/src/index.d.ts
+++ b/src/index.d.ts
@@ -137,7 +137,8 @@ export {
   GraphQLWrappingType,
   GraphQLNullableType,
   GraphQLNamedType,
-  Thunk,
+  ThunkArray,
+  ThunkObjMap,
   GraphQLSchemaConfig,
   GraphQLSchemaExtensions,
   GraphQLDirectiveConfig,
diff --git a/src/index.js b/src/index.js
index 5d3be4b8b0..cd446b7fd5 100644
--- a/src/index.js
+++ b/src/index.js
@@ -136,7 +136,8 @@ export type {
   GraphQLWrappingType,
   GraphQLNullableType,
   GraphQLNamedType,
-  Thunk,
+  ThunkArray,
+  ThunkObjMap,
   GraphQLSchemaConfig,
   GraphQLDirectiveConfig,
   GraphQLArgument,
diff --git a/src/jsutils/ObjMap.d.ts b/src/jsutils/ObjMap.d.ts
new file mode 100644
index 0000000000..29f31fae66
--- /dev/null
+++ b/src/jsutils/ObjMap.d.ts
@@ -0,0 +1,7 @@
+export type ObjMap<T> = Record<string, T>;
+export type ObjMapLike<T> = ObjMap<T> | Record<string, T>;
+
+export type ReadOnlyObjMap<T> = Readonly<Record<string, T>>;
+export type ReadOnlyObjMapLike<T> =
+  | Readonly<Record<string, T>>
+  | ReadOnlyObjMap<T>;
diff --git a/src/type/definition.d.ts b/src/type/definition.d.ts
index 69150e727f..2f085c9c8a 100644
--- a/src/type/definition.d.ts
+++ b/src/type/definition.d.ts
@@ -5,6 +5,7 @@ import { Maybe } from '../jsutils/Maybe';
 
 import { PromiseOrValue } from '../jsutils/PromiseOrValue';
 import { Path } from '../jsutils/Path';
+import { ObjMap } from '../jsutils/ObjMap';
 
 import {
   ScalarTypeDefinitionNode,
@@ -263,9 +264,8 @@ export function getNamedType(type: GraphQLType): GraphQLNamedType;
  * Used while defining GraphQL types to allow for circular references in
  * otherwise immutable type definitions.
  */
-export type Thunk<T extends { [key: string]: any } | Array<any>> =
-  | (() => T)
-  | T;
+export type ThunkArray<T> = Array<T> | (() => Array<T>);
+export type ThunkObjMap<T> = ObjMap<T> | (() => ObjMap<T>);
 
 /**
  * Custom extensions
@@ -435,8 +435,8 @@ export function argsToArgsConfig(
 export interface GraphQLObjectTypeConfig<TSource, TContext> {
   name: string;
   description?: Maybe<string>;
-  interfaces?: Thunk<Array<GraphQLInterfaceType>>;
-  fields: Thunk<GraphQLFieldConfigMap<TSource, TContext>>;
+  interfaces?: ThunkArray<GraphQLInterfaceType>;
+  fields: ThunkObjMap<GraphQLFieldConfig<TSource, TContext>>;
   isTypeOf?: Maybe<GraphQLIsTypeOfFn<TSource, TContext>>;
   extensions?: Maybe<Readonly<GraphQLObjectTypeExtensions<TSource, TContext>>>;
   astNode?: Maybe<ObjectTypeDefinitionNode>;
@@ -637,8 +637,8 @@ export class GraphQLInterfaceType {
 export interface GraphQLInterfaceTypeConfig<TSource, TContext> {
   name: string;
   description?: Maybe<string>;
-  interfaces?: Thunk<Array<GraphQLInterfaceType>>;
-  fields: Thunk<GraphQLFieldConfigMap<TSource, TContext>>;
+  interfaces?: ThunkArray<GraphQLInterfaceType>;
+  fields: ThunkObjMap<GraphQLFieldConfig<TSource, TContext>>;
   /**
    * Optionally provide a custom type resolver function. If one is not provided,
    * the default implementation will call `isTypeOf` on each implementing
@@ -711,7 +711,7 @@ export class GraphQLUnionType {
 export interface GraphQLUnionTypeConfig<TSource, TContext> {
   name: string;
   description?: Maybe<string>;
-  types: Thunk<Array<GraphQLObjectType>>;
+  types: ThunkArray<GraphQLObjectType>;
   /**
    * Optionally provide a custom type resolver function. If one is not provided,
    * the default implementation will call `isTypeOf` on each implementing
@@ -884,7 +884,7 @@ export class GraphQLInputObjectType {
 export interface GraphQLInputObjectTypeConfig {
   name: string;
   description?: Maybe<string>;
-  fields: Thunk<GraphQLInputFieldConfigMap>;
+  fields: ThunkObjMap<GraphQLInputFieldConfig>;
   extensions?: Maybe<Readonly<GraphQLInputObjectTypeExtensions>>;
   astNode?: Maybe<InputObjectTypeDefinitionNode>;
   extensionASTNodes?: Maybe<ReadonlyArray<InputObjectTypeExtensionNode>>;
diff --git a/src/type/definition.js b/src/type/definition.js
index ed24c7f57a..02fccdd82d 100644
--- a/src/type/definition.js
+++ b/src/type/definition.js
@@ -511,9 +511,14 @@ export function getNamedType(type) {
  * Used while defining GraphQL types to allow for circular references in
  * otherwise immutable type definitions.
  */
-export type Thunk<+T: ObjMap<any> | Array<any>> = (() => T) | T;
+export type ThunkArray<T> = (() => Array<T>) | Array<T>;
+export type ThunkObjMap<T> = (() => ObjMap<T>) | ObjMap<T>;
 
-function resolveThunk<+T: ObjMap<any> | Array<any>>(thunk: Thunk<T>): T {
+function resolveArrayThunk<T>(thunk: ThunkArray<T>): Array<T> {
+  return typeof thunk === 'function' ? thunk() : thunk;
+}
+
+function resolveObjMapThunk<T>(thunk: ThunkObjMap<T>): ObjMap<T> {
   return typeof thunk === 'function' ? thunk() : thunk;
 }
 
@@ -703,8 +708,8 @@ export class GraphQLObjectType {
   astNode: ?ObjectTypeDefinitionNode;
   extensionASTNodes: ?$ReadOnlyArray<ObjectTypeExtensionNode>;
 
-  _fields: Thunk<GraphQLFieldMap<any, any>>;
-  _interfaces: Thunk<Array<GraphQLInterfaceType>>;
+  _fields: ThunkObjMap<GraphQLField<any, any>>;
+  _interfaces: ThunkArray<GraphQLInterfaceType>;
 
   constructor(config: $ReadOnly<GraphQLObjectTypeConfig<any, any>>) {
     this.name = config.name;
@@ -771,7 +776,7 @@ function defineInterfaces(
     | GraphQLInterfaceTypeConfig<mixed, mixed>,
   >,
 ): Array<GraphQLInterfaceType> {
-  const interfaces = resolveThunk(config.interfaces ?? []);
+  const interfaces = resolveArrayThunk(config.interfaces ?? []);
   devAssert(
     Array.isArray(interfaces),
     `${config.name} interfaces must be an Array or a function which returns an Array.`,
@@ -785,7 +790,7 @@ function defineFieldMap<TSource, TContext>(
     | GraphQLInterfaceTypeConfig<TSource, TContext>,
   >,
 ): GraphQLFieldMap<TSource, TContext> {
-  const fieldMap = resolveThunk(config.fields);
+  const fieldMap = resolveObjMapThunk(config.fields);
   devAssert(
     isPlainObj(fieldMap),
     `${config.name} fields must be an object with field names as keys or a function which returns such an object.`,
@@ -874,8 +879,8 @@ export function argsToArgsConfig(
 export type GraphQLObjectTypeConfig<TSource, TContext> = {|
   name: string,
   description?: ?string,
-  interfaces?: Thunk<Array<GraphQLInterfaceType>>,
-  fields: Thunk<GraphQLFieldConfigMap<TSource, TContext>>,
+  interfaces?: ThunkArray<GraphQLInterfaceType>,
+  fields: ThunkObjMap<GraphQLFieldConfig<TSource, TContext>>,
   isTypeOf?: ?GraphQLIsTypeOfFn<TSource, TContext>,
   extensions?: ?ReadOnlyObjMapLike<mixed>,
   astNode?: ?ObjectTypeDefinitionNode,
@@ -1020,8 +1025,8 @@ export class GraphQLInterfaceType {
   astNode: ?InterfaceTypeDefinitionNode;
   extensionASTNodes: ?$ReadOnlyArray<InterfaceTypeExtensionNode>;
 
-  _fields: Thunk<GraphQLFieldMap<any, any>>;
-  _interfaces: Thunk<Array<GraphQLInterfaceType>>;
+  _fields: ThunkObjMap<GraphQLField<any, any>>;
+  _interfaces: ThunkArray<GraphQLInterfaceType>;
 
   constructor(config: $ReadOnly<GraphQLInterfaceTypeConfig<any, any>>) {
     this.name = config.name;
@@ -1085,8 +1090,8 @@ export class GraphQLInterfaceType {
 export type GraphQLInterfaceTypeConfig<TSource, TContext> = {|
   name: string,
   description?: ?string,
-  interfaces?: Thunk<Array<GraphQLInterfaceType>>,
-  fields: Thunk<GraphQLFieldConfigMap<TSource, TContext>>,
+  interfaces?: ThunkArray<GraphQLInterfaceType>,
+  fields: ThunkObjMap<GraphQLFieldConfig<TSource, TContext>>,
   /**
    * Optionally provide a custom type resolver function. If one is not provided,
    * the default implementation will call `isTypeOf` on each implementing
@@ -1137,7 +1142,7 @@ export class GraphQLUnionType {
   astNode: ?UnionTypeDefinitionNode;
   extensionASTNodes: ?$ReadOnlyArray<UnionTypeExtensionNode>;
 
-  _types: Thunk<Array<GraphQLObjectType>>;
+  _types: ThunkArray<GraphQLObjectType>;
 
   constructor(config: $ReadOnly<GraphQLUnionTypeConfig<any, any>>) {
     this.name = config.name;
@@ -1192,7 +1197,7 @@ export class GraphQLUnionType {
 function defineTypes(
   config: $ReadOnly<GraphQLUnionTypeConfig<mixed, mixed>>,
 ): Array<GraphQLObjectType> {
-  const types = resolveThunk(config.types);
+  const types = resolveArrayThunk(config.types);
   devAssert(
     Array.isArray(types),
     `Must provide Array of types or a function which returns such an array for Union ${config.name}.`,
@@ -1203,7 +1208,7 @@ function defineTypes(
 export type GraphQLUnionTypeConfig<TSource, TContext> = {|
   name: string,
   description?: ?string,
-  types: Thunk<Array<GraphQLObjectType>>,
+  types: ThunkArray<GraphQLObjectType>,
   /**
    * Optionally provide a custom type resolver function. If one is not provided,
    * the default implementation will call `isTypeOf` on each implementing
@@ -1463,7 +1468,7 @@ export class GraphQLInputObjectType {
   astNode: ?InputObjectTypeDefinitionNode;
   extensionASTNodes: ?$ReadOnlyArray<InputObjectTypeExtensionNode>;
 
-  _fields: Thunk<GraphQLInputFieldMap>;
+  _fields: ThunkObjMap<GraphQLInputField>;
 
   constructor(config: $ReadOnly<GraphQLInputObjectTypeConfig>) {
     this.name = config.name;
@@ -1519,7 +1524,7 @@ export class GraphQLInputObjectType {
 function defineInputFieldMap(
   config: $ReadOnly<GraphQLInputObjectTypeConfig>,
 ): GraphQLInputFieldMap {
-  const fieldMap = resolveThunk(config.fields);
+  const fieldMap = resolveObjMapThunk(config.fields);
   devAssert(
     isPlainObj(fieldMap),
     `${config.name} fields must be an object with field names as keys or a function which returns such an object.`,
@@ -1545,7 +1550,7 @@ function defineInputFieldMap(
 export type GraphQLInputObjectTypeConfig = {|
   name: string,
   description?: ?string,
-  fields: Thunk<GraphQLInputFieldConfigMap>,
+  fields: ThunkObjMap<GraphQLInputFieldConfig>,
   extensions?: ?ReadOnlyObjMapLike<mixed>,
   astNode?: ?InputObjectTypeDefinitionNode,
   extensionASTNodes?: ?$ReadOnlyArray<InputObjectTypeExtensionNode>,
diff --git a/src/type/index.d.ts b/src/type/index.d.ts
index 9686f413b7..f226df5651 100644
--- a/src/type/index.d.ts
+++ b/src/type/index.d.ts
@@ -73,7 +73,8 @@ export {
   GraphQLWrappingType,
   GraphQLNullableType,
   GraphQLNamedType,
-  Thunk,
+  ThunkArray,
+  ThunkObjMap,
   GraphQLArgument,
   GraphQLArgumentConfig,
   GraphQLArgumentExtensions,
diff --git a/src/type/index.js b/src/type/index.js
index 811d50247a..6bcef9daed 100644
--- a/src/type/index.js
+++ b/src/type/index.js
@@ -128,7 +128,8 @@ export type {
   GraphQLWrappingType,
   GraphQLNullableType,
   GraphQLNamedType,
-  Thunk,
+  ThunkArray,
+  ThunkObjMap,
   GraphQLArgument,
   GraphQLArgumentConfig,
   GraphQLEnumTypeConfig,