diff --git a/src/sound/apu.js b/src/sound/apu.js
index 596276e..d64fa04 100644
--- a/src/sound/apu.js
+++ b/src/sound/apu.js
@@ -9,7 +9,7 @@ var APU = function(memory) {
     this.memory = memory;
     this.enabled = false;
 
-    AudioContext = window.AudioContext || window.webkitAudioContext;
+    var AudioContext = window.AudioContext || window.webkitAudioContext;
     var audioContext = new AudioContext();
 
     this.channel1 = new GameboyJS.Channel1(this, 1, audioContext);