--- a/DeviceGraphicsContext.st	Wed Feb 01 21:42:41 2017 +0000
+++ b/DeviceGraphicsContext.st	Wed Feb 01 22:17:58 2017 +0000
@@ -587,7 +587,7 @@
     (aForm ~~ mask) ifTrue:[
         mask := aForm.
         gcId notNil ifTrue:[
-            (mask == nil) ifTrue:[
+            mask isNil ifTrue:[
                 device setBitmapMask:nil in:gcId
             ] ifFalse:[
                 mask := mask asFormOn:device.