diff --git a/msgpack5/index.d.ts b/msgpack5/index.d.ts
index 361f817514..ceb02cc758 100644
--- a/msgpack5/index.d.ts
+++ b/msgpack5/index.d.ts
@@ -1,7 +1,6 @@
 // Type definitions for msgpack5 v3.4.0
 // Project: https://github.com/mcollina/msgpack5/
-// Definitions by: Wonshik Kim <https://github.com/wokim/>
-// Definitions by: Kei Son <https://github.com/heycalmdown/>
+// Definitions by: Wonshik Kim <https://github.com/wokim/>, Kei Son <https://github.com/heycalmdown/>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 import stream = require('stream');
diff --git a/msgpack5/tsconfig.json b/msgpack5/tsconfig.json
index 5a4cfa1259..82e4af0f63 100644
--- a/msgpack5/tsconfig.json
+++ b/msgpack5/tsconfig.json
@@ -4,7 +4,7 @@
         "moduleResolution": "node",
         "target": "es6",
         "noImplicitAny": true,
-        "strictNullChecks": false,
+        "strictNullChecks": true,
         "baseUrl": "../",
         "typeRoots": [
             "../"