diff --git a/js/perf/core.js b/js/perf/core.js
index 6b3b27475..cc41c5867 100644
--- a/js/perf/core.js
+++ b/js/perf/core.js
@@ -1,5 +1,7 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 
+const System = imports.system;
+
 const Main = imports.ui.main;
 const Scripting = imports.ui.scripting;
 
@@ -99,7 +101,7 @@ function run() {
         Main.overview.hide();
         yield Scripting.waitLeisure();
 
-        global.gc();
+        System.gc();
         yield Scripting.sleep(1000);
         Scripting.collectStatistics();
         Scripting.scriptEvent('afterShowHide');
diff --git a/js/ui/lookingGlass.js b/js/ui/lookingGlass.js
index df994f117..3e6a086f7 100644
--- a/js/ui/lookingGlass.js
+++ b/js/ui/lookingGlass.js
@@ -12,6 +12,7 @@ const Shell = imports.gi.Shell;
 const Signals = imports.signals;
 const Lang = imports.lang;
 const Mainloop = imports.mainloop;
+const System = imports.system;
 
 const History = imports.misc.history;
 const ExtensionSystem = imports.ui.extensionSystem;
@@ -665,7 +666,7 @@ const Memory = new Lang.Class({
 
         this._gcbutton = new St.Button({ label: 'Full GC',
                                          style_class: 'lg-obj-inspector-button' });
-        this._gcbutton.connect('clicked', Lang.bind(this, function () { global.gc(); this._renderText(); }));
+        this._gcbutton.connect('clicked', Lang.bind(this, function () { System.gc(); this._renderText(); }));
         this.actor.add(this._gcbutton, { x_align: St.Align.START,
                                          x_fill: false });