diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index b32f6960a2..e21fb784f2 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -615,6 +615,9 @@ static void do_trap(struct cpu_user_regs *regs, int use_error_code)
     unsigned int trapnr = regs->entry_vector;
     unsigned long fixup;
 
+    if ( regs->error_code & X86_XEC_EXT )
+        goto hardware_trap;
+
     DEBUGGER_trap_entry(trapnr, regs);
 
     if ( guest_mode(regs) )
@@ -641,6 +644,7 @@ static void do_trap(struct cpu_user_regs *regs, int use_error_code)
         return;
     }
 
+ hardware_trap:
     DEBUGGER_trap_fatal(trapnr, regs);
 
     show_execution_state(regs);
@@ -1262,13 +1266,14 @@ static int handle_gdt_ldt_mapping_fault(
             tb = propagate_page_fault(curr->arch.pv_vcpu.ldt_base + offset,
                                       regs->error_code);
             if ( tb )
-                tb->error_code = ((u16)offset & ~3) | 4;
+                tb->error_code = (offset & ~(X86_XEC_EXT | X86_XEC_IDT)) |
+                                 X86_XEC_TI;
         }
     }
     else
     {
         /* GDT fault: handle the fault as #GP(selector). */
-        regs->error_code = (u16)offset & ~7;
+        regs->error_code = offset & ~(X86_XEC_EXT | X86_XEC_IDT | X86_XEC_TI);
         (void)do_general_protection(regs);
     }
 
@@ -3221,7 +3226,7 @@ void do_general_protection(struct cpu_user_regs *regs)
 
     DEBUGGER_trap_entry(TRAP_gp_fault, regs);
 
-    if ( regs->error_code & 1 )
+    if ( regs->error_code & X86_XEC_EXT )
         goto hardware_gp;
 
     if ( !guest_mode(regs) )
@@ -3240,14 +3245,15 @@ void do_general_protection(struct cpu_user_regs *regs)
      * 
      * Instead, a GPF occurs with the faulting IDT vector in the error code.
      * Bit 1 is set to indicate that an IDT entry caused the fault. Bit 0 is 
-     * clear to indicate that it's a software fault, not hardware.
+     * clear (which got already checked above) to indicate that it's a software
+     * fault, not a hardware one.
      * 
      * NOTE: Vectors 3 and 4 are dealt with from their own handler. This is
      * okay because they can only be triggered by an explicit DPL-checked
      * instruction. The DPL specified by the guest OS for these vectors is NOT
      * CHECKED!!
      */
-    if ( (regs->error_code & 3) == 2 )
+    if ( regs->error_code & X86_XEC_IDT )
     {
         /* This fault must be due to <INT n> instruction. */
         const struct trap_info *ti;
@@ -3289,9 +3295,9 @@ void do_general_protection(struct cpu_user_regs *regs)
         return;
     }
 
+ hardware_gp:
     DEBUGGER_trap_fatal(TRAP_gp_fault, regs);
 
- hardware_gp:
     show_execution_state(regs);
     panic("GENERAL PROTECTION FAULT\n[error_code=%04x]", regs->error_code);
 }
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index d4dd8e8114..94a54aa7f2 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -338,7 +338,7 @@ int80_slow_path:
          * Setup entry vector and error code as if this was a GPF caused by an
          * IDT entry with DPL==0.
          */
-        movl  $((0x80 << 3) | 0x2),UREGS_error_code(%rsp)
+        movl  $((0x80 << 3) | X86_XEC_IDT),UREGS_error_code(%rsp)
         SAVE_PRESERVED
         movl  $TRAP_gp_fault,UREGS_entry_vector(%rsp)
         /* A GPF wouldn't have incremented the instruction pointer. */
diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index fcfa7ddc5d..a40c18ee0a 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -143,6 +143,11 @@
 #define PFEC_page_paged     (1U<<5)
 #define PFEC_page_shared    (1U<<6)
 
+/* Other exception error code values. */
+#define X86_XEC_EXT         (_AC(1,U) << 0)
+#define X86_XEC_IDT         (_AC(1,U) << 1)
+#define X86_XEC_TI          (_AC(1,U) << 2)
+
 #define XEN_MINIMAL_CR4 (X86_CR4_PGE | X86_CR4_PAE)
 
 #define XEN_SYSCALL_MASK (X86_EFLAGS_AC|X86_EFLAGS_VM|X86_EFLAGS_RF|    \