--- a/DisplaySurface.st	Wed Apr 20 09:06:30 2016 +0100
+++ b/DisplaySurface.st	Thu Apr 21 08:01:58 2016 +0100
@@ -1014,6 +1014,8 @@
 
     |oldPaint org patternOffsetX patternOffsetY|
 
+    viewBackground isNil ifTrue:[^ self]. "/ how can this happen?
+
     viewBackground isColor ifFalse:[
 	viewBackground isViewBackground ifTrue:[
 	    oldPaint := self paint.