Index: cont.c
===================================================================
--- cont.c	(revision 31345)
+++ cont.c	(working copy)
@@ -285,6 +285,7 @@
     /* save thread context */
     cont->saved_thread = *th;
     cont->saved_thread.local_storage = 0;
+    cont->saved_thread.machine_stack_start = cont->saved_thread.machine_stack_end = 0;
 }
 
 static rb_context_t *