diff --git a/types/graphql-errors/graphql-errors-tests.ts b/types/graphql-errors/graphql-errors-tests.ts
index 0820fe2afa..d9d07b2071 100644
--- a/types/graphql-errors/graphql-errors-tests.ts
+++ b/types/graphql-errors/graphql-errors-tests.ts
@@ -2,7 +2,7 @@ import { GraphQLSchema, buildSchema } from 'graphql';
 import {
     UserError,
     maskErrors,
-    handlerFunction,
+    HandlerFunction,
     setDefaultHandler
 } from 'graphql-errors';
 
@@ -11,7 +11,7 @@ const schema: GraphQLSchema = buildSchema(`
   # graphql schema definition
 `);
 
-const customHandler: handlerFunction = err => {
+const customHandler: HandlerFunction = err => {
     return { ...err, message: 'Internal error' };
 };
 
diff --git a/types/graphql-errors/index.d.ts b/types/graphql-errors/index.d.ts
index 5dc452ab20..d179cf3d7e 100644
--- a/types/graphql-errors/index.d.ts
+++ b/types/graphql-errors/index.d.ts
@@ -6,11 +6,11 @@
 
 import { GraphQLSchema } from 'graphql';
 
-export type handlerFunction = (err: Error) => Error;
+export type HandlerFunction = (err: Error) => Error;
 
-export function setDefaultHandler(fn: handlerFunction): void;
+export function setDefaultHandler(fn: HandlerFunction): void;
 
-export function maskErrors(schema: GraphQLSchema, fn?: handlerFunction): void;
+export function maskErrors(schema: GraphQLSchema, fn?: HandlerFunction): void;
 
 export class UserError extends Error {
     constructor(message: string);