diff --git a/src/build.tsx b/src/build.tsx
index ab26572..57967db 100644
--- a/src/build.tsx
+++ b/src/build.tsx
@@ -112,4 +112,4 @@ fs.cpSync("src/static", "out/static", { recursive: true });
if (environment == "dev") {
fs.cpSync("src/static_dev", "out/static/dev", { recursive: true });
}
-fs.writeFileSync("out/index.html", html);
+fs.writeFileSync("out/index.html", `<!DOCTYPE html>${html}`);