diff --git a/kernel/trunk/boot/bootcode.inc b/kernel/trunk/boot/bootcode.inc
index 40983c6532..02c35b5bff 100644
--- a/kernel/trunk/boot/bootcode.inc
+++ b/kernel/trunk/boot/bootcode.inc
@@ -830,7 +830,8 @@ end if
 if defined extended_primary_loader
         sub     ax, [preboot_timeout]
 else
-        sub     ax, 18*5
+        ; bios 0x1A timer runs at ~18 ticks per second
+        sub     ax, 18*PREBOOT_TIMEOUT
 end if
         jae     .timergo
         neg     ax
diff --git a/kernel/trunk/boot/preboot.inc b/kernel/trunk/boot/preboot.inc
index d91a55f338..b47a8c94e1 100644
--- a/kernel/trunk/boot/preboot.inc
+++ b/kernel/trunk/boot/preboot.inc
@@ -31,7 +31,8 @@ preboot_device      db  0 ; boot device
                           ;!!!! 0 - autodetect !!!!
 preboot_biosdisk    db  0 ; use V86 to access disks through BIOS (1-yes, 2-no)
 if defined extended_primary_loader
-preboot_timeout     dw  5*18 ; timeout in 1/18th of second for config settings screen
+; timeout in 1/18th of second for config settings screen
+preboot_timeout     dw  PREBOOT_TIMEOUT*18
 end if
 
       if $>0x200
diff --git a/kernel/trunk/bootbios.asm b/kernel/trunk/bootbios.asm
index 260a2ddb45..7039a6769f 100644
--- a/kernel/trunk/bootbios.asm
+++ b/kernel/trunk/bootbios.asm
@@ -11,6 +11,7 @@ include 'encoding.inc'
 include 'const.inc'
 
 os_code = code_l - tmp_gdt
+PREBOOT_TIMEOUT = 5   ; seconds
 
 use16
                   org   0x0