diff --git a/includes/templates/LegacySidebar.mustache b/includes/templates/LegacySidebar.mustache
index 066f6b4a3..7b4de7b20 100644
--- a/includes/templates/LegacySidebar.mustache
+++ b/includes/templates/LegacySidebar.mustache
@@ -1,8 +1,7 @@
 {{!
 	See @typedef SidebarData
 }}
-
-<div id="mw-panel">
+<div id="mw-panel" class="vector-legacy-sidebar">
 	<div id="p-logo" role="banner">
 		<a class="mw-wiki-logo" href="{{link-mainpage}}"
 			title="{{msg-tooltip-p-logo}}"></a>
diff --git a/resources/skins.vector.styles.legacy/components/MenuPortal.less b/resources/skins.vector.styles.legacy/components/LegacySidebar.less
similarity index 90%
rename from resources/skins.vector.styles.legacy/components/MenuPortal.less
rename to resources/skins.vector.styles.legacy/components/LegacySidebar.less
index cdce25bef..81db52f7a 100644
--- a/resources/skins.vector.styles.legacy/components/MenuPortal.less
+++ b/resources/skins.vector.styles.legacy/components/LegacySidebar.less
@@ -1,6 +1,8 @@
 @import '../../common/variables.less';
 @import 'mediawiki.mixins.less';
 
+// FIXME: Remove `.vector-menu-portal` selector when cached HTML not a problem.
+.vector-legacy-sidebar .vector-menu-portal,
 .vector-menu-portal {
 	margin: 0 @margin-end-portal  0 @margin-start-portal;
 	padding: 0.25em 0;
diff --git a/resources/skins.vector.styles.legacy/skin-legacy.less b/resources/skins.vector.styles.legacy/skin-legacy.less
index 0d3942df2..2160db55e 100644
--- a/resources/skins.vector.styles.legacy/skin-legacy.less
+++ b/resources/skins.vector.styles.legacy/skin-legacy.less
@@ -11,7 +11,7 @@
 	@import './components/Menu.less';
 	@import './components/MenuDropdown.less';
 	@import './components/MenuTabs.less';
-	@import './components/MenuPortal.less';
+	@import './components/LegacySidebar.less';
 	@import './components/SearchBox.less';
 	@import './components/Sidebar.less';
 	@import './components/TabWatchstarLink.less';