diff --git a/build.html b/build.html
index 7c31d38..338e025 100644
--- a/build.html
+++ b/build.html
@@ -121,7 +121,7 @@ function onLoad(initial) {
function onOsChanged(initial) {
var os = document.getElementById('osSelect').value;
if (os.includes('Choose ')) {
- if (history.state != '') {
+ if (history.state !== '' && history.state !== null) {
history.pushState('', '', 'build.html');
}