--- a/ProcessorScheduler.st	Thu Nov 05 20:20:09 1998 +0100
+++ b/ProcessorScheduler.st	Mon Nov 09 21:19:41 1998 +0100
@@ -2663,6 +2663,8 @@
     |index "{ Class: SmallInteger }"
      wasBlocked|
 
+    aBlock isNil ifTrue:[^ self].
+
     wasBlocked := OperatingSystem blockInterrupts.
     index := timeoutActionArray identityIndexOf:aBlock startingAt:1.
     (index ~~ 0) ifTrue:[
@@ -2997,6 +2999,6 @@
 !ProcessorScheduler class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/ProcessorScheduler.st,v 1.167 1998-10-01 11:00:06 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/ProcessorScheduler.st,v 1.168 1998-11-09 20:19:41 cg Exp $'
 ! !
 ProcessorScheduler initialize!