diff --git a/bochs/cpu/access.cc b/bochs/cpu/access.cc
index 3293c9bf5..a5495d324 100644
--- a/bochs/cpu/access.cc
+++ b/bochs/cpu/access.cc
@@ -1,5 +1,5 @@
 /////////////////////////////////////////////////////////////////////////
-// $Id: access.cc,v 1.101 2008-04-27 19:48:57 sshwarts Exp $
+// $Id: access.cc,v 1.102 2008-05-01 05:11:19 sshwarts Exp $
 /////////////////////////////////////////////////////////////////////////
 //
 //  Copyright (C) 2001  MandrakeSoft S.A.
@@ -121,6 +121,11 @@ BX_CPU_C::write_virtual_checks(bx_segment_reg_t *seg, bx_address offset, unsigne
     return;
   }
   else { /* real mode */
+    if (seg->cache.valid==0) {
+      BX_DEBUG(("write_virtual_checks(): segment descriptor not valid (real mode)"));
+      exception(int_number(seg), 0, 0);
+    }
+
     if (offset > (seg->cache.u.segment.limit_scaled - length + 1)
           || (length-1 > seg->cache.u.segment.limit_scaled))
     {
@@ -211,6 +216,11 @@ BX_CPU_C::read_virtual_checks(bx_segment_reg_t *seg, bx_address offset, unsigned
     return;
   }
   else { /* real mode */
+    if (seg->cache.valid==0) {
+      BX_DEBUG(("read_virtual_checks(): segment descriptor not valid (real mode)"));
+      exception(int_number(seg), 0, 0);
+    }
+
     if (offset > (seg->cache.u.segment.limit_scaled - length + 1)
         || (length-1 > seg->cache.u.segment.limit_scaled))
     {
@@ -305,6 +315,11 @@ BX_CPU_C::execute_virtual_checks(bx_segment_reg_t *seg, bx_address offset, unsig
     return;
   }
   else { /* real mode */
+    if (seg->cache.valid==0) {
+      BX_DEBUG(("execute_virtual_checks(): segment descriptor not valid (real mode)"));
+      exception(int_number(seg), 0, 0);
+    }
+
     if (offset > (seg->cache.u.segment.limit_scaled - length + 1)
         || (length-1 > seg->cache.u.segment.limit_scaled))
     {