--- a/AbstractOperatingSystem.st	Thu Oct 27 16:36:21 2011 +0200
+++ b/AbstractOperatingSystem.st	Thu Oct 27 18:31:24 2011 +0200
@@ -5520,7 +5520,10 @@
     |sum|
 
     sum := msTime1 + msTime2.
-    (sum > 16r1FFFFFFF) ifTrue:[^ sum - 16r20000000].
+    (sum > 16r1FFFFFFF) ifTrue:[
+        self assert:(sum <= 16r3FFFFFFF) message:'overflow in timer computation'.
+        ^ sum - 16r20000000.
+    ].
     (sum < 0) ifTrue:[^ sum + 16r20000000].
     ^ sum
 !
@@ -7055,11 +7058,11 @@
 !AbstractOperatingSystem class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/AbstractOperatingSystem.st,v 1.214 2011-08-05 16:19:00 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/AbstractOperatingSystem.st,v 1.215 2011-10-27 16:31:24 stefan Exp $'
 !
 
 version_CVS
-    ^ '$Header: /cvs/stx/stx/libbasic/AbstractOperatingSystem.st,v 1.214 2011-08-05 16:19:00 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/AbstractOperatingSystem.st,v 1.215 2011-10-27 16:31:24 stefan Exp $'
 ! !
 
 AbstractOperatingSystem initialize!