diff --git a/core/isolinux.asm b/core/isolinux.asm
index bd4e9556922d..c4db4133e274 100644
--- a/core/isolinux.asm
+++ b/core/isolinux.asm
@@ -420,7 +420,7 @@ MaxLMA		equ 384*1024		; Reasonable limit (384K)
 		call getlinsec
 		pop eax
 		pop cx
-		mov dx,cx
+		movzx edx,cx
 		pop bp
 		pop bx