diff --git a/src/arch/x86/mmap_boot.c b/src/arch/x86/mmap_boot.c
index 0c2b45dd18..ae35451b3c 100644
--- a/src/arch/x86/mmap_boot.c
+++ b/src/arch/x86/mmap_boot.c
@@ -55,8 +55,9 @@ static int cbfs_master_header_props(struct cbfs_props *props)
 
 	props->offset = header.offset;
 	if (CONFIG_ROM_SIZE != header.romsize)
-		props->offset += CONFIG_ROM_SIZE - header.romsize;
-	props->size = CONFIG_ROM_SIZE;
+		props->size = CONFIG_ROM_SIZE;
+	else
+		props->size = header.romsize;
 	props->size -= props->offset;
 	props->size -= header.bootblocksize;
 	props->size = ALIGN_DOWN(props->size, 64);