diff --git a/src/jsutils/ObjMap.ts b/src/jsutils/ObjMap.ts
index 2c20282187..fb70be09ed 100644
--- a/src/jsutils/ObjMap.ts
+++ b/src/jsutils/ObjMap.ts
@@ -1,13 +1,13 @@
 export interface ObjMap<T> {
-  [key: string]: T;
+  [key: string | symbol]: T;
 }
 
-export type ObjMapLike<T> = ObjMap<T> | { [key: string]: T };
+export type ObjMapLike<T> = ObjMap<T> | { [key: string | symbol]: T };
 
 export interface ReadOnlyObjMap<T> {
-  readonly [key: string]: T;
+  readonly [key: string | symbol]: T;
 }
 
 export type ReadOnlyObjMapLike<T> =
   | ReadOnlyObjMap<T>
-  | { readonly [key: string]: T };
+  | { readonly [key: string | symbol]: T };
diff --git a/src/type/definition.ts b/src/type/definition.ts
index 5e0c6d0472..e69be9882b 100644
--- a/src/type/definition.ts
+++ b/src/type/definition.ts
@@ -552,7 +552,7 @@ export function resolveObjMapThunk<T>(thunk: ThunkObjMap<T>): ObjMap<T> {
  * an object which can contain all the values you need.
  */
 export interface GraphQLScalarTypeExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 /**
@@ -1031,7 +1031,7 @@ export type GraphQLFieldConfigArgumentMap = ObjMap<GraphQLArgumentConfig>;
  * an object which can contain all the values you need.
  */
 export interface GraphQLArgumentExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 export interface GraphQLArgumentConfig {
@@ -1087,7 +1087,7 @@ export type GraphQLFieldMap<TSource, TContext> = ObjMap<
  * an object which can contain all the values you need.
  */
 export interface GraphQLInterfaceTypeExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 /**
@@ -1211,7 +1211,7 @@ export interface GraphQLInterfaceTypeNormalizedConfig
  * an object which can contain all the values you need.
  */
 export interface GraphQLUnionTypeExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 /**
@@ -1339,7 +1339,7 @@ interface GraphQLUnionTypeNormalizedConfig
  * an object which can contain all the values you need.
  */
 export interface GraphQLEnumTypeExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 /**
@@ -1551,7 +1551,7 @@ export type GraphQLEnumValueConfigMap /* <T> */ =
  * an object which can contain all the values you need.
  */
 export interface GraphQLEnumValueExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 export interface GraphQLEnumValueConfig {
@@ -1581,7 +1581,7 @@ export interface GraphQLEnumValue {
  * an object which can contain all the values you need.
  */
 export interface GraphQLInputObjectTypeExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 /**
@@ -1716,7 +1716,7 @@ interface GraphQLInputObjectTypeNormalizedConfig
  * an object which can contain all the values you need.
  */
 export interface GraphQLInputFieldExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 export interface GraphQLInputFieldConfig {
diff --git a/src/type/directives.ts b/src/type/directives.ts
index bb3e441a43..eab15272fe 100644
--- a/src/type/directives.ts
+++ b/src/type/directives.ts
@@ -46,7 +46,7 @@ export function assertDirective(directive: unknown): GraphQLDirective {
  * an object which can contain all the values you need.
  */
 export interface GraphQLDirectiveExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 /**
diff --git a/src/type/schema.ts b/src/type/schema.ts
index 97c2782145..af968f4ea7 100644
--- a/src/type/schema.ts
+++ b/src/type/schema.ts
@@ -54,9 +54,10 @@ export function assertSchema(schema: unknown): GraphQLSchema {
  * your library or project. Do not use a shortened identifier as this increases
  * the risk of conflicts. We recommend you add at most one extension field,
  * an object which can contain all the values you need.
+ * Conflicts can be avoided by using a symbol instead of a string key.
  */
 export interface GraphQLSchemaExtensions {
-  [attributeName: string]: unknown;
+  [attributeName: string | symbol]: unknown;
 }
 
 /**