diff --git a/src/theme/index.hbs b/src/theme/index.hbs
index 37a029b587..6f3948c652 100644
--- a/src/theme/index.hbs
+++ b/src/theme/index.hbs
@@ -92,10 +92,12 @@
         <!-- Hide / unhide sidebar before it is displayed -->
         <script>
             var html = document.querySelector('html');
-            var sidebar = 'hidden';
+            var sidebar = null;
             if (document.body.clientWidth >= 1080) {
                 try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
                 sidebar = sidebar || 'visible';
+            } else {
+                sidebar = 'hidden';
             }
             html.classList.remove('sidebar-visible');
             html.classList.add("sidebar-" + sidebar);