diff --git a/bochs/cpu/cpu.cc b/bochs/cpu/cpu.cc
index 7f5ad8f67..b462b0e5c 100644
--- a/bochs/cpu/cpu.cc
+++ b/bochs/cpu/cpu.cc
@@ -1,5 +1,5 @@
 /////////////////////////////////////////////////////////////////////////
-// $Id: cpu.cc,v 1.241 2008-09-24 10:39:35 sshwarts Exp $
+// $Id: cpu.cc,v 1.242 2008-09-26 20:41:41 sshwarts Exp $
 /////////////////////////////////////////////////////////////////////////
 //
 //  Copyright (C) 2001  MandrakeSoft S.A.
@@ -573,7 +573,15 @@ unsigned BX_CPU_C::handleAsyncEvent(void)
         // boundary. (becomes a trap)
         if (! (BX_CPU_THIS_PTR inhibit_mask & BX_INHIBIT_DEBUG)) {
           // Commit debug events to DR6
-          BX_CPU_THIS_PTR dr6 = BX_CPU_THIS_PTR debug_trap;
+#if BX_CPU_LEVEL <= 4
+          // On 386/486 bit12 is settable
+          BX_CPU_THIS_PTR dr6 = (BX_CPU_THIS_PTR dr6 & 0xffff0ff0) |
+                            (BX_CPU_THIS_PTR debug_trap & 0x0000f00f);
+#else
+          // On Pentium+, bit12 is always zero
+          BX_CPU_THIS_PTR dr6 = (BX_CPU_THIS_PTR dr6 & 0xffff0ff0) |
+                            (BX_CPU_THIS_PTR debug_trap & 0x0000e00f);
+#endif
           exception(BX_DB_EXCEPTION, 0, 0); // no error, not interrupt
         }
       }