diff --git a/src/asio_server_request_handler.cc b/src/asio_server_request_handler.cc
index 52e56e59..14eec64e 100644
--- a/src/asio_server_request_handler.cc
+++ b/src/asio_server_request_handler.cc
@@ -36,7 +36,7 @@ std::string create_html(int status_code) {
std::string res;
res.reserve(512);
auto status = ::nghttp2::http2::get_status_string(status_code);
- res += "";
+ res += R"(<!DOCTYPE html><html lang="en"><title>)";
res += status;
res += "";
res += status;
diff --git a/src/shrpx_http.cc b/src/shrpx_http.cc
index 5867c02c..c3f1aa7b 100644
--- a/src/shrpx_http.cc
+++ b/src/shrpx_http.cc
@@ -39,7 +39,7 @@ std::string create_error_html(unsigned int status_code) {
std::string res;
res.reserve(512);
auto status = http2::get_status_string(status_code);
- res += "";
+ res += R"(<!DOCTYPE html><html lang="en"><title>)";
res += status;
res += "";
res += status;