diff --git a/examples/typescript-001/src/app/app.tsx b/examples/typescript-001/src/app/app.tsx
index d04aeab..be0ac0d 100644
--- a/examples/typescript-001/src/app/app.tsx
+++ b/examples/typescript-001/src/app/app.tsx
@@ -20,7 +20,7 @@ export default function App() {
           change {history.index + 1} / {history.nodes.length}
         </span>
         <span>|</span>
-        <span>{getCurrentChangeDate().toISOString()}</span>
+        <span>{getCurrentChangeDate()?.toISOString()}</span>
       </div>
       <div className="editor">
         <textarea value={value.text} rows={4} onChange={update} />
diff --git a/tsconfig.base.json b/tsconfig.base.json
index c4d31e2..7ce7251 100644
--- a/tsconfig.base.json
+++ b/tsconfig.base.json
@@ -13,6 +13,9 @@
     "lib": ["es2020", "dom"],
     "skipLibCheck": true,
     "skipDefaultLibCheck": true,
+    "strict": true,
+    "strictNullChecks": true,
+    "noUncheckedIndexedAccess": true,
     "baseUrl": ".",
     "paths": {
       "valtio-history": ["packages/history-utility/src/index.ts"]