diff --git a/Cocoa/GBWindow.m b/Cocoa/GBWindow.m
index 4b4e273..ef17df1 100644
--- a/Cocoa/GBWindow.m
+++ b/Cocoa/GBWindow.m
@@ -13,7 +13,7 @@
 - (void)_zoomFill:(id)sender
 {
     if (sender == [self standardWindowButton:NSWindowZoomButton] &&
-        (self.currentEvent.modifierFlags & NSEventModifierFlagOption)) {
+        ((self.currentEvent.modifierFlags & NSEventModifierFlagDeviceIndependentFlagsMask) == NSEventModifierFlagOption)) {
         [self zoom:sender];
         return;
     }