diff --git a/package.json b/package.json
index 8c8b81f77..e2ece33a0 100644
--- a/package.json
+++ b/package.json
@@ -149,13 +149,6 @@
       }
     },
     "preset": "ts-jest",
-    "globals": {
-      "ts-jest": {
-        "tsconfig": {
-          "target": "es6"
-        }
-      }
-    },
     "globalSetup": "./tests/global-setup.ts",
     "setupFilesAfterEnv": [
       "./tests/setup.ts"
diff --git a/src/utils/errors.ts b/src/utils/errors.ts
index ee1353666..5665ed609 100644
--- a/src/utils/errors.ts
+++ b/src/utils/errors.ts
@@ -8,6 +8,7 @@ import { HttpError } from 'http-errors';
 export class AccessTokenError extends Error {
   public code: string;
 
+  /* istanbul ignore next */
   constructor(code: string, message: string) {
     super(message);
 
@@ -19,6 +20,7 @@ export class AccessTokenError extends Error {
 
     // Machine readable code.
     this.code = code;
+    Object.setPrototypeOf(this, AccessTokenError.prototype);
   }
 }
 
@@ -48,6 +50,7 @@ export class HandlerError extends Error {
   public status: number | undefined;
   public code: string | undefined;
 
+  /* istanbul ignore next */
   constructor(error: Error | AccessTokenError | HttpError) {
     super(htmlSafe(error.message));
 
@@ -60,5 +63,6 @@ export class HandlerError extends Error {
     if ('status' in error) {
       this.status = error.status;
     }
+    Object.setPrototypeOf(this, HandlerError.prototype);
   }
 }
diff --git a/tests/utils/errors.test.ts b/tests/utils/errors.test.ts
new file mode 100644
index 000000000..8bc1392bf
--- /dev/null
+++ b/tests/utils/errors.test.ts
@@ -0,0 +1,8 @@
+import { AccessTokenError, HandlerError } from '../../src/utils/errors';
+
+describe('errors', () => {
+  test('should be instance of themselves', () => {
+    expect(new AccessTokenError('code', 'message')).toBeInstanceOf(AccessTokenError);
+    expect(new HandlerError(new Error('message'))).toBeInstanceOf(HandlerError);
+  });
+});