diff --git a/resources/Resources.php b/resources/Resources.php
index a5bfbc512cf..9d6ce523418 100644
--- a/resources/Resources.php
+++ b/resources/Resources.php
@@ -947,6 +947,7 @@ return [
 		],
 		'dependencies' => [
 			'jquery.footHovzer',
+			'oojs-ui-core',
 		],
 	],
 	'mediawiki.diff.styles' => [
diff --git a/resources/src/mediawiki/mediawiki.debug.js b/resources/src/mediawiki/mediawiki.debug.js
index 939b84122fa..830ff339f64 100644
--- a/resources/src/mediawiki/mediawiki.debug.js
+++ b/resources/src/mediawiki/mediawiki.debug.js
@@ -4,6 +4,15 @@
 	var debug,
 		hovzer = $.getFootHovzer();
 
+	OO.ui.getViewportSpacing = function () {
+		return {
+			top: 0,
+			right: 0,
+			bottom: hovzer.$.outerHeight(),
+			left: 0
+		};
+	};
+
 	/**
 	 * Debug toolbar.
 	 *