diff --git a/src/error/GraphQLError.ts b/src/error/GraphQLError.ts
index 7fec9608830..2bb3ccb7cd4 100644
--- a/src/error/GraphQLError.ts
+++ b/src/error/GraphQLError.ts
@@ -29,6 +29,14 @@ export interface GraphQLErrorOptions {
   extensions?: Maybe<GraphQLErrorExtensions>;
 }
 
+const isGraphQLErrorSymbol = Symbol.for('GraphQLError');
+
+export function isGraphQLError(error: unknown): error is GraphQLError {
+  return (
+    typeof error === 'object' && error != null && isGraphQLErrorSymbol in error
+  );
+}
+
 /**
  * A GraphQLError describes an Error found during the parse, validate, or
  * execute phases of performing a GraphQL operation. In addition to a message
@@ -36,6 +44,7 @@ export interface GraphQLErrorOptions {
  * GraphQL document and/or execution result that correspond to the Error.
  */
 export class GraphQLError extends Error {
+  [isGraphQLErrorSymbol]: true = true;
   /**
    * An array of `{ line, column }` locations within the source GraphQL document
    * which correspond to this error.
diff --git a/src/execution/subscribe.ts b/src/execution/subscribe.ts
index 7a04480bf44..ac601cac454 100644
--- a/src/execution/subscribe.ts
+++ b/src/execution/subscribe.ts
@@ -3,7 +3,7 @@ import { isAsyncIterable } from '../jsutils/isAsyncIterable';
 import type { Maybe } from '../jsutils/Maybe';
 import { addPath, pathToArray } from '../jsutils/Path';
 
-import { GraphQLError } from '../error/GraphQLError';
+import { GraphQLError, isGraphQLError } from '../error/GraphQLError';
 import { locatedError } from '../error/locatedError';
 
 import type { DocumentNode } from '../language/ast';
@@ -169,7 +169,7 @@ export async function createSourceEventStream(
   } catch (error) {
     // If it GraphQLError, report it as an ExecutionResult, containing only errors and no data.
     // Otherwise treat the error as a system-class error and re-throw it.
-    if (error instanceof GraphQLError) {
+    if (isGraphQLError(error)) {
       return { errors: [error] };
     }
     throw error;
diff --git a/src/language/source.ts b/src/language/source.ts
index 15f65fceeec..f45b6afc60d 100644
--- a/src/language/source.ts
+++ b/src/language/source.ts
@@ -1,12 +1,13 @@
 import { devAssert } from '../jsutils/devAssert';
 import { inspect } from '../jsutils/inspect';
-import { instanceOf } from '../jsutils/instanceOf';
 
 interface Location {
   line: number;
   column: number;
 }
 
+const isSourceSymbol = Symbol.for('Source');
+
 /**
  * A representation of source input to GraphQL. The `name` and `locationOffset` parameters are
  * optional, but they are useful for clients who store GraphQL documents in source files.
@@ -15,6 +16,7 @@ interface Location {
  * The `line` and `column` properties in `locationOffset` are 1-indexed.
  */
 export class Source {
+  [isSourceSymbol]: true = true;
   body: string;
   name: string;
   locationOffset: Location;
@@ -53,5 +55,7 @@ export class Source {
  * @internal
  */
 export function isSource(source: unknown): source is Source {
-  return instanceOf(source, Source);
+  return (
+    typeof source === 'object' && source != null && isSourceSymbol in source
+  );
 }
diff --git a/src/type/definition.ts b/src/type/definition.ts
index 9eea02e8eaf..c8c0ec06baf 100644
--- a/src/type/definition.ts
+++ b/src/type/definition.ts
@@ -2,7 +2,6 @@ import { devAssert } from '../jsutils/devAssert';
 import { didYouMean } from '../jsutils/didYouMean';
 import { identityFunc } from '../jsutils/identityFunc';
 import { inspect } from '../jsutils/inspect';
-import { instanceOf } from '../jsutils/instanceOf';
 import { isObjectLike } from '../jsutils/isObjectLike';
 import { keyMap } from '../jsutils/keyMap';
 import { keyValMap } from '../jsutils/keyValMap';
@@ -75,11 +74,17 @@ export function assertType(type: unknown): GraphQLType {
   return type;
 }
 
+const isGraphQLScalarTypeSymbol = Symbol.for('GraphQLScalarType');
+
 /**
  * There are predicates for each kind of GraphQL type.
  */
 export function isScalarType(type: unknown): type is GraphQLScalarType {
-  return instanceOf(type, GraphQLScalarType);
+  return (
+    typeof type === 'object' &&
+    type != null &&
+    isGraphQLScalarTypeSymbol in type
+  );
 }
 
 export function assertScalarType(type: unknown): GraphQLScalarType {
@@ -89,8 +94,14 @@ export function assertScalarType(type: unknown): GraphQLScalarType {
   return type;
 }
 
+const isGraphQLObjectTypeSymbol = Symbol.for('GraphQLObjectType');
+
 export function isObjectType(type: unknown): type is GraphQLObjectType {
-  return instanceOf(type, GraphQLObjectType);
+  return (
+    typeof type === 'object' &&
+    type != null &&
+    isGraphQLObjectTypeSymbol in type
+  );
 }
 
 export function assertObjectType(type: unknown): GraphQLObjectType {
@@ -100,8 +111,14 @@ export function assertObjectType(type: unknown): GraphQLObjectType {
   return type;
 }
 
+const isGraphQLInterfaceTypeSymbol = Symbol.for('GraphQLInterfaceType');
+
 export function isInterfaceType(type: unknown): type is GraphQLInterfaceType {
-  return instanceOf(type, GraphQLInterfaceType);
+  return (
+    typeof type === 'object' &&
+    type != null &&
+    isGraphQLInterfaceTypeSymbol in type
+  );
 }
 
 export function assertInterfaceType(type: unknown): GraphQLInterfaceType {
@@ -113,8 +130,12 @@ export function assertInterfaceType(type: unknown): GraphQLInterfaceType {
   return type;
 }
 
+const isGraphQLUnionTypeSymbol = Symbol.for('GraphQLUnionType');
+
 export function isUnionType(type: unknown): type is GraphQLUnionType {
-  return instanceOf(type, GraphQLUnionType);
+  return (
+    typeof type === 'object' && type != null && isGraphQLUnionTypeSymbol in type
+  );
 }
 
 export function assertUnionType(type: unknown): GraphQLUnionType {
@@ -124,8 +145,12 @@ export function assertUnionType(type: unknown): GraphQLUnionType {
   return type;
 }
 
+const isGraphQLEnumTypeSymbol = Symbol.for('GraphQLEnumType');
+
 export function isEnumType(type: unknown): type is GraphQLEnumType {
-  return instanceOf(type, GraphQLEnumType);
+  return (
+    typeof type === 'object' && type != null && isGraphQLEnumTypeSymbol in type
+  );
 }
 
 export function assertEnumType(type: unknown): GraphQLEnumType {
@@ -135,10 +160,16 @@ export function assertEnumType(type: unknown): GraphQLEnumType {
   return type;
 }
 
+const isGraphQLInputObjectTypeSymbol = Symbol.for('GraphQLInputObjectType');
+
 export function isInputObjectType(
   type: unknown,
 ): type is GraphQLInputObjectType {
-  return instanceOf(type, GraphQLInputObjectType);
+  return (
+    typeof type === 'object' &&
+    type != null &&
+    isGraphQLInputObjectTypeSymbol in type
+  );
 }
 
 export function assertInputObjectType(type: unknown): GraphQLInputObjectType {
@@ -150,6 +181,8 @@ export function assertInputObjectType(type: unknown): GraphQLInputObjectType {
   return type;
 }
 
+const isGraphQLListTypeSymbol = Symbol.for('GraphQLListType');
+
 export function isListType(
   type: GraphQLInputType,
 ): type is GraphQLList<GraphQLInputType>;
@@ -158,7 +191,9 @@ export function isListType(
 ): type is GraphQLList<GraphQLOutputType>;
 export function isListType(type: unknown): type is GraphQLList<GraphQLType>;
 export function isListType(type: unknown): type is GraphQLList<GraphQLType> {
-  return instanceOf(type, GraphQLList);
+  return (
+    typeof type === 'object' && type != null && isGraphQLListTypeSymbol in type
+  );
 }
 
 export function assertListType(type: unknown): GraphQLList<GraphQLType> {
@@ -168,6 +203,8 @@ export function assertListType(type: unknown): GraphQLList<GraphQLType> {
   return type;
 }
 
+const isGraphQLNonNullTypeSymbol = Symbol.for('GraphQLNonNullType');
+
 export function isNonNullType(
   type: GraphQLInputType,
 ): type is GraphQLNonNull<GraphQLNullableInputType>;
@@ -180,7 +217,11 @@ export function isNonNullType(
 export function isNonNullType(
   type: unknown,
 ): type is GraphQLNonNull<GraphQLNullableType> {
-  return instanceOf(type, GraphQLNonNull);
+  return (
+    typeof type === 'object' &&
+    type != null &&
+    isGraphQLNonNullTypeSymbol in type
+  );
 }
 
 export function assertNonNullType(type: unknown): GraphQLNonNull<GraphQLType> {
@@ -319,6 +360,7 @@ export function assertAbstractType(type: unknown): GraphQLAbstractType {
  * ```
  */
 export class GraphQLList<T extends GraphQLType> {
+  readonly [isGraphQLListTypeSymbol]: true = true;
   readonly ofType: T;
 
   constructor(ofType: T) {
@@ -365,6 +407,7 @@ export class GraphQLList<T extends GraphQLType> {
  * Note: the enforcement of non-nullability occurs within the executor.
  */
 export class GraphQLNonNull<T extends GraphQLNullableType> {
+  readonly [isGraphQLNonNullTypeSymbol]: true = true;
   readonly ofType: T;
 
   constructor(ofType: T) {
@@ -555,6 +598,7 @@ export interface GraphQLScalarTypeExtensions {
  * ```
  */
 export class GraphQLScalarType<TInternal = unknown, TExternal = TInternal> {
+  readonly [isGraphQLScalarTypeSymbol]: true = true;
   name: string;
   description: Maybe<string>;
   specifiedByURL: Maybe<string>;
@@ -725,6 +769,7 @@ export interface GraphQLObjectTypeExtensions<_TSource = any, _TContext = any> {
  * ```
  */
 export class GraphQLObjectType<TSource = any, TContext = any> {
+  readonly [isGraphQLObjectTypeSymbol]: true = true;
   name: string;
   description: Maybe<string>;
   isTypeOf: Maybe<GraphQLIsTypeOfFn<TSource, TContext>>;
@@ -1078,6 +1123,7 @@ export interface GraphQLInterfaceTypeExtensions {
  * ```
  */
 export class GraphQLInterfaceType {
+  readonly [isGraphQLInterfaceTypeSymbol]: true = true;
   name: string;
   description: Maybe<string>;
   resolveType: Maybe<GraphQLTypeResolver<any, any>>;
@@ -1207,6 +1253,7 @@ export interface GraphQLUnionTypeExtensions {
  * ```
  */
 export class GraphQLUnionType {
+  readonly [isGraphQLUnionTypeSymbol]: true = true;
   name: string;
   description: Maybe<string>;
   resolveType: Maybe<GraphQLTypeResolver<any, any>>;
@@ -1334,6 +1381,7 @@ export interface GraphQLEnumTypeExtensions {
  * will be used as its internal value.
  */
 export class GraphQLEnumType /* <T> */ {
+  readonly [isGraphQLEnumTypeSymbol]: true = true;
   name: string;
   description: Maybe<string>;
   extensions: Readonly<GraphQLEnumTypeExtensions>;
@@ -1574,6 +1622,7 @@ export interface GraphQLInputObjectTypeExtensions {
  * ```
  */
 export class GraphQLInputObjectType {
+  readonly [isGraphQLInputObjectTypeSymbol]: true = true;
   name: string;
   description: Maybe<string>;
   extensions: Readonly<GraphQLInputObjectTypeExtensions>;
diff --git a/src/type/directives.ts b/src/type/directives.ts
index bb3e441a433..aa28a8f7c98 100644
--- a/src/type/directives.ts
+++ b/src/type/directives.ts
@@ -1,6 +1,5 @@
 import { devAssert } from '../jsutils/devAssert';
 import { inspect } from '../jsutils/inspect';
-import { instanceOf } from '../jsutils/instanceOf';
 import { isObjectLike } from '../jsutils/isObjectLike';
 import type { Maybe } from '../jsutils/Maybe';
 import { toObjMap } from '../jsutils/toObjMap';
@@ -24,7 +23,11 @@ import { GraphQLBoolean, GraphQLString } from './scalars';
  * Test if the given value is a GraphQL directive.
  */
 export function isDirective(directive: unknown): directive is GraphQLDirective {
-  return instanceOf(directive, GraphQLDirective);
+  return (
+    typeof directive === 'object' &&
+    directive != null &&
+    isGraphQLDirectiveSymbol in directive
+  );
 }
 
 export function assertDirective(directive: unknown): GraphQLDirective {
@@ -49,11 +52,14 @@ export interface GraphQLDirectiveExtensions {
   [attributeName: string]: unknown;
 }
 
+const isGraphQLDirectiveSymbol = Symbol.for('GraphQLDirective');
+
 /**
  * Directives are used by the GraphQL runtime as a way of modifying execution
  * behavior. Type system creators will usually not create these directly.
  */
 export class GraphQLDirective {
+  [isGraphQLDirectiveSymbol]: true = true;
   name: string;
   description: Maybe<string>;
   locations: ReadonlyArray<DirectiveLocation>;
diff --git a/src/type/schema.ts b/src/type/schema.ts
index 7cc576a18f9..dde9d44c68a 100644
--- a/src/type/schema.ts
+++ b/src/type/schema.ts
@@ -1,6 +1,5 @@
 import { devAssert } from '../jsutils/devAssert';
 import { inspect } from '../jsutils/inspect';
-import { instanceOf } from '../jsutils/instanceOf';
 import { isObjectLike } from '../jsutils/isObjectLike';
 import type { Maybe } from '../jsutils/Maybe';
 import type { ObjMap } from '../jsutils/ObjMap';
@@ -43,7 +42,9 @@ import {
  * Test if the given value is a GraphQL schema.
  */
 export function isSchema(schema: unknown): schema is GraphQLSchema {
-  return instanceOf(schema, GraphQLSchema);
+  return (
+    typeof schema === 'object' && schema != null && isSchemaSymbol in schema
+  );
 }
 
 export function assertSchema(schema: unknown): GraphQLSchema {
@@ -66,6 +67,8 @@ export interface GraphQLSchemaExtensions {
   [attributeName: string]: unknown;
 }
 
+const isSchemaSymbol = Symbol.for('GraphQLSchema');
+
 /**
  * Schema Definition
  *
@@ -139,6 +142,7 @@ export class GraphQLSchema {
   extensions: Readonly<GraphQLSchemaExtensions>;
   astNode: Maybe<SchemaDefinitionNode>;
   extensionASTNodes: ReadonlyArray<SchemaExtensionNode>;
+  [isSchemaSymbol]: true = true;
 
   // Used as a cache for validateSchema().
   __validationErrors: Maybe<ReadonlyArray<GraphQLError>>;
diff --git a/src/utilities/coerceInputValue.ts b/src/utilities/coerceInputValue.ts
index 136bee63c9e..3c15162308b 100644
--- a/src/utilities/coerceInputValue.ts
+++ b/src/utilities/coerceInputValue.ts
@@ -8,7 +8,7 @@ import { addPath, pathToArray } from '../jsutils/Path';
 import { printPathArray } from '../jsutils/printPathArray';
 import { suggestionList } from '../jsutils/suggestionList';
 
-import { GraphQLError } from '../error/GraphQLError';
+import { GraphQLError, isGraphQLError } from '../error/GraphQLError';
 
 import type { GraphQLInputType } from '../type/definition';
 import {
@@ -154,7 +154,7 @@ function coerceInputValueImpl(
     try {
       parseResult = type.parseValue(inputValue);
     } catch (error) {
-      if (error instanceof GraphQLError) {
+      if (isGraphQLError(error)) {
         onError(pathToArray(path), inputValue, error);
       } else {
         onError(
diff --git a/src/validation/rules/ValuesOfCorrectTypeRule.ts b/src/validation/rules/ValuesOfCorrectTypeRule.ts
index 5d81a3833a0..cee21489194 100644
--- a/src/validation/rules/ValuesOfCorrectTypeRule.ts
+++ b/src/validation/rules/ValuesOfCorrectTypeRule.ts
@@ -3,7 +3,7 @@ import { inspect } from '../../jsutils/inspect';
 import { keyMap } from '../../jsutils/keyMap';
 import { suggestionList } from '../../jsutils/suggestionList';
 
-import { GraphQLError } from '../../error/GraphQLError';
+import { GraphQLError, isGraphQLError } from '../../error/GraphQLError';
 
 import type { ValueNode } from '../../language/ast';
 import { print } from '../../language/printer';
@@ -138,7 +138,7 @@ function isValidValueNode(context: ValidationContext, node: ValueNode): void {
     }
   } catch (error) {
     const typeStr = inspect(locationType);
-    if (error instanceof GraphQLError) {
+    if (isGraphQLError(error)) {
       context.reportError(error);
     } else {
       context.reportError(