diff --git a/sys/boot/i386/btx/btx/btx.S b/sys/boot/i386/btx/btx/btx.S
index 334bea6f6c8a..04bbdca2f2f0 100644
--- a/sys/boot/i386/btx/btx/btx.S
+++ b/sys/boot/i386/btx/btx/btx.S
@@ -862,7 +862,7 @@ ifdef(`PAGING',`
 ')
 		popl %eax			# Call
 		call *%eax			#  program
-intx30.1:	incb %ss:btx_hdr+0x7		# Flag reboot
+intx30.1:	orb $0x1,%ss:btx_hdr+0x7	# Flag reboot
 		jmp exit			# Exit
 #
 # Dump structure [EBX] to [EDI], using format string [ESI].
diff --git a/sys/boot/i386/btx/btx/btx.s b/sys/boot/i386/btx/btx/btx.s
index 334bea6f6c8a..04bbdca2f2f0 100644
--- a/sys/boot/i386/btx/btx/btx.s
+++ b/sys/boot/i386/btx/btx/btx.s
@@ -862,7 +862,7 @@ ifdef(`PAGING',`
 ')
 		popl %eax			# Call
 		call *%eax			#  program
-intx30.1:	incb %ss:btx_hdr+0x7		# Flag reboot
+intx30.1:	orb $0x1,%ss:btx_hdr+0x7	# Flag reboot
 		jmp exit			# Exit
 #
 # Dump structure [EBX] to [EDI], using format string [ESI].