diff --git a/src/boot.asm b/src/boot.asm
index e08a042..908329a 100644
--- a/src/boot.asm
+++ b/src/boot.asm
@@ -1,6 +1,6 @@
 %define MAGIC       0xe85250d6
 %define ARCH        0
-%define LEN         (header_end - header_start)
+%define LEN         header_end - header_start
 %define CHECKSUM    -(MAGIC + ARCH + LEN)
 
 header_start: