diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 7b784f4..6d4f7ba 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1025,7 +1025,7 @@
 
 ENTRY(xen_hypervisor_callback)
 	CFI_STARTPROC
-	pushl_cfi $0
+	pushl_cfi $-1 /* orig_ax = -1 => not a system call */
 	SAVE_ALL
 	TRACE_IRQS_OFF
 
@@ -1067,14 +1067,16 @@
 2:	mov 8(%esp),%es
 3:	mov 12(%esp),%fs
 4:	mov 16(%esp),%gs
+	/* EAX == 0 => Category 1 (Bad segment)
+	   EAX != 0 => Category 2 (Bad IRET) */
 	testl %eax,%eax
 	popl_cfi %eax
 	lea 16(%esp),%esp
 	CFI_ADJUST_CFA_OFFSET -16
 	jz 5f
 	addl $16,%esp
-	jmp iret_exc		# EAX != 0 => Category 2 (Bad IRET)
-5:	pushl_cfi $0		# EAX == 0 => Category 1 (Bad segment)
+	jmp iret_exc
+5:	pushl_cfi $-1 /* orig_ax = -1 => not a system call */
 	SAVE_ALL
 	jmp ret_from_exception
 	CFI_ENDPROC
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index cdc79b5..bd6f592 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1351,7 +1351,7 @@
 	CFI_RESTORE r11
 	addq $0x30,%rsp
 	CFI_ADJUST_CFA_OFFSET -0x30
-	pushq_cfi $0
+	pushq_cfi $-1 /* orig_ax = -1 => not a system call */
 	SAVE_ALL
 	jmp error_exit
 	CFI_ENDPROC