diff --git a/readme.md b/readme.md
index ef3a8ff..25985b4 100644
--- a/readme.md
+++ b/readme.md
@@ -76,12 +76,12 @@ import {jsonObject, jsonMember, TypedJSON} from 'typedjson';
 import * as Decimal from 'decimal.js'; // Or any other library your type originates from
 
 TypedJSON.mapType(BigInt, {
-    deserializer: json => value == null ? value : new BigInt(json),
+    deserializer: json => json == null ? json : BigInt(json),
     serializer: value => value == null ? value : value.toString(),
 });
 
 TypedJSON.mapType(Decimal, {
-    deserializer: json => value == null ? value : new Decimal(json),
+    deserializer: json => json == null ? json : new Decimal(json),
     serializer: value => value == null ? value : value.toString(),
 });
 
@@ -89,7 +89,7 @@ TypedJSON.mapType(Decimal, {
 class MappedTypes {
 
     @jsonMember
-    cryptoKey: BigInt;
+    cryptoKey: bigint;
 
     @jsonMember
     money: Decimal;