diff --git a/ace/index.html b/ace/index.html
index 4ef36f4..9a5c80b 100644
--- a/ace/index.html
+++ b/ace/index.html
@@ -100,7 +100,7 @@
             });
 
             function toggleFullscreen() {
-                if (window.fullScreen) {
+                if (!window.fullScreen) {
                     var elem = document.documentElement;
                     if (elem.requestFullscreen) {
                         elem.requestFullscreen();