@@ -, +, @@ 
---
 libguile/threads.c |   19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)
--- guile-1.8.5.orig/libguile/threads.c	2008-11-13 15:17:12.000000000 -0600
+++ guile-1.8.5.orig/libguile/threads.c	2008-11-13 15:32:07.000000000 -0600
@@ -577,9 +577,24 @@ scm_i_init_thread_for_guile (SCM_STACKIT
       /* This thread is already guilified but not in guile mode, just
 	 resume it.
 	 
-	 XXX - base might be lower than when this thread was first
-	 guilified.
+         A user call to scm_with_guile() will lead us to here. This
+         could happen anywhere on the stack, and in particular, the
+         stack can be *much* shorter than what it was when this thread
+         was first guilified. This will typically happen in
+         on_thread_exit(), where the stack is *always* shorter than
+         when the thread was first guilified. If the GC happens to
+         get triggered due to some other thread, we'd end up with
+         t->top "upside-down" w.r.t. t->base, which will result in
+         chaos in scm_threads_mark_stacks() when top-base=2^32 or 2^64.
+         Thus, reset the base, if needed.
        */
+#if SCM_STACK_GROWS_UP
+      if (base < t->base)
+         t->base = base;
+#else
+      if (base > t->base)
+         t->base = base;
+#endif
       scm_enter_guile ((scm_t_guile_ticket) t);
       return 1;
     }