diff --git a/src/execution/__tests__/union-interface-test.ts b/src/execution/__tests__/union-interface-test.ts
index b7691fa689..6f8408c487 100644
--- a/src/execution/__tests__/union-interface-test.ts
+++ b/src/execution/__tests__/union-interface-test.ts
@@ -1,6 +1,8 @@
 import { expect } from 'chai';
 import { describe, it } from 'mocha';
 
+import { expectJSON } from '../../__testUtils__/expectJSON.js';
+
 import { parse } from '../../language/parser.js';
 
 import {
@@ -12,7 +14,7 @@ import {
 import { GraphQLBoolean, GraphQLString } from '../../type/scalars.js';
 import { GraphQLSchema } from '../../type/schema.js';
 
-import { executeSync } from '../execute.js';
+import { execute, executeSync } from '../execute.js';
 
 class Dog {
   name: string;
@@ -42,19 +44,30 @@ class Cat {
   }
 }
 
+class Plant {
+  name: string;
+
+  constructor(name: string) {
+    this.name = name;
+  }
+}
+
 class Person {
   name: string;
   pets: ReadonlyArray<Dog | Cat> | undefined;
   friends: ReadonlyArray<Dog | Cat | Person> | undefined;
+  responsibilities: ReadonlyArray<Dog | Cat | Plant> | undefined;
 
   constructor(
     name: string,
     pets?: ReadonlyArray<Dog | Cat>,
     friends?: ReadonlyArray<Dog | Cat | Person>,
+    responsibilities?: ReadonlyArray<Dog | Cat | Plant>,
   ) {
     this.name = name;
     this.pets = pets;
     this.friends = friends;
+    this.responsibilities = responsibilities;
   }
 }
 
@@ -108,6 +121,18 @@ const CatType: GraphQLObjectType = new GraphQLObjectType({
   isTypeOf: (value) => value instanceof Cat,
 });
 
+const PlantType: GraphQLObjectType = new GraphQLObjectType({
+  name: 'Plant',
+  interfaces: [NamedType],
+  fields: () => ({
+    name: { type: GraphQLString },
+  }),
+  // eslint-disable-next-line @typescript-eslint/require-await
+  isTypeOf: async () => {
+    throw new Error('Not sure if this is a plant');
+  },
+});
+
 const PetType = new GraphQLUnionType({
   name: 'Pet',
   types: [DogType, CatType],
@@ -124,6 +149,11 @@ const PetType = new GraphQLUnionType({
   },
 });
 
+const PetOrPlantType = new GraphQLUnionType({
+  name: 'PetOrPlantType',
+  types: [PlantType, DogType, CatType],
+});
+
 const PersonType: GraphQLObjectType = new GraphQLObjectType({
   name: 'Person',
   interfaces: [NamedType, MammalType, LifeType],
@@ -131,6 +161,7 @@ const PersonType: GraphQLObjectType = new GraphQLObjectType({
     name: { type: GraphQLString },
     pets: { type: new GraphQLList(PetType) },
     friends: { type: new GraphQLList(NamedType) },
+    responsibilities: { type: new GraphQLList(PetOrPlantType) },
     progeny: { type: new GraphQLList(PersonType) },
     mother: { type: PersonType },
     father: { type: PersonType },
@@ -151,8 +182,14 @@ const odie = new Dog('Odie', true);
 odie.mother = new Dog("Odie's Mom", true);
 odie.mother.progeny = [odie];
 
+const fern = new Plant('Fern');
 const liz = new Person('Liz');
-const john = new Person('John', [garfield, odie], [liz, odie]);
+const john = new Person(
+  'John',
+  [garfield, odie],
+  [liz, odie],
+  [garfield, fern],
+);
 
 describe('Execute: Union and intersection types', () => {
   it('can introspect on union and intersection types', () => {
@@ -195,7 +232,12 @@ describe('Execute: Union and intersection types', () => {
           name: 'Named',
           fields: [{ name: 'name' }],
           interfaces: [],
-          possibleTypes: [{ name: 'Dog' }, { name: 'Cat' }, { name: 'Person' }],
+          possibleTypes: [
+            { name: 'Dog' },
+            { name: 'Cat' },
+            { name: 'Person' },
+            { name: 'Plant' },
+          ],
           enumValues: null,
           inputFields: null,
         },
@@ -545,4 +587,50 @@ describe('Execute: Union and intersection types', () => {
     expect(encounteredRootValue).to.equal(rootValue);
     expect(encounteredContext).to.equal(contextValue);
   });
+
+  it('it handles rejections from isTypeOf after after an isTypeOf returns true', async () => {
+    const document = parse(`
+      {
+        responsibilities {
+          __typename
+          ... on Dog {
+            name
+            barks
+          }
+          ... on Cat {
+            name
+            meows
+          }
+        }
+      }
+    `);
+
+    const rootValue = new Person('John', [], [liz], [garfield]);
+    const contextValue = { authToken: '123abc' };
+
+    /* c8 ignore next 4 */
+    // eslint-disable-next-line no-undef
+    process.on('unhandledRejection', () => {
+      expect.fail('Unhandled rejection');
+    });
+
+    const result = await execute({
+      schema,
+      document,
+      rootValue,
+      contextValue,
+    });
+
+    expectJSON(result).toDeepEqual({
+      data: {
+        responsibilities: [
+          {
+            __typename: 'Cat',
+            meows: false,
+            name: 'Garfield',
+          },
+        ],
+      },
+    });
+  });
 });
diff --git a/src/execution/execute.ts b/src/execution/execute.ts
index acc3f86040..97a8eb76ac 100644
--- a/src/execution/execute.ts
+++ b/src/execution/execute.ts
@@ -1823,6 +1823,12 @@ export const defaultTypeResolver: GraphQLTypeResolver<unknown, unknown> =
         if (isPromise(isTypeOfResult)) {
           promisedIsTypeOfResults[i] = isTypeOfResult;
         } else if (isTypeOfResult) {
+          if (promisedIsTypeOfResults.length > 0) {
+            Promise.all(promisedIsTypeOfResults).then(undefined, () => {
+              /* ignore errors */
+            });
+          }
+
           return type.name;
         }
       }