Index: /trunk/src/VBox/Main/src-client/GuestCtrlImplTasks.cpp
===================================================================
--- /trunk/src/VBox/Main/src-client/GuestCtrlImplTasks.cpp	(revision 39693)
+++ /trunk/src/VBox/Main/src-client/GuestCtrlImplTasks.cpp	(revision 39694)
@@ -577,6 +577,6 @@
                                 }
 
+                                Assert(cbToRead >= aOutputData.size());
                                 cbToRead -= aOutputData.size();
-                                Assert(cbToRead >= 0);
                                 cbTransfered += aOutputData.size();