diff --git a/js/misc/util.js b/js/misc/util.js
index 314d7660f..2da489bbe 100644
--- a/js/misc/util.js
+++ b/js/misc/util.js
@@ -1,7 +1,7 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 /* exported findUrls, spawn, spawnCommandLine, spawnApp, trySpawnCommandLine,
             formatTime, formatTimeSpan, createTimeLabel, insertSorted,
-            ensureActorVisibleInScrollView, wiggle */
+            ensureActorVisibleInScrollView, wiggle, lerp */
 
 const { Clutter, Gio, GLib, Shell, St, GnomeDesktop } = imports.gi;
 const Gettext = imports.gettext;
@@ -435,3 +435,7 @@ function wiggle(actor, params) {
         },
     });
 }
+
+function lerp(start, end, progress) {
+    return start + progress * (end - start);
+}