diff --git a/bios/8086.asm b/bios/8086.asm
index 6600127..594dff9 100644
--- a/bios/8086.asm
+++ b/bios/8086.asm
@@ -162,7 +162,7 @@ SETTRK:
   RET
 
 SETSEC:
-  AND WORD [DISKCX], 0xFFA0
+  AND WORD [DISKCX], 0xFFC0
   OR BYTE [DISKCX], CL
   RET