diff --git a/assets/gitbook/custom.css b/assets/gitbook/custom.css
index 1497b4c2bc..7379f6d0a3 100644
--- a/assets/gitbook/custom.css
+++ b/assets/gitbook/custom.css
@@ -13,6 +13,7 @@
 .book.with-summary .book-body .book-header {
     position: fixed;
     width: calc(100% - 300px);
+    overflow-x: hidden;
     overflow-y: hidden;
 }