Index: usr.bin/mkubootimage/mkubootimage.c
===================================================================
RCS file: /cvsroot/src/usr.bin/mkubootimage/mkubootimage.c,v
retrieving revision 1.27
diff -u -p -r1.27 mkubootimage.c
--- usr.bin/mkubootimage/mkubootimage.c	7 Dec 2019 12:34:17 -0000	1.27
+++ usr.bin/mkubootimage/mkubootimage.c	1 Jan 2020 10:11:56 -0000
@@ -334,7 +334,8 @@ generate_header_uimg(struct uboot_image_
 		iov[2].iov_len = st.st_size;
 		crc = crc32v(iov, 3);
 	} else {
-		dsize = st.st_size;
+		dsize = update_image ?
+		    st.st_size - sizeof(*hdr) : st.st_size;
 		crc = crc32(p, st.st_size);
 	}
 	munmap(p, st.st_size);
@@ -387,10 +388,13 @@ generate_header_arm64(struct arm64_image
 	flags |= ARM64_FLAGS_PHYS_PLACEMENT_ANY;
 #endif
 
+	const uint64_t dsize = update_image ?
+	   st.st_size - sizeof(*hdr) : st.st_size;
+
 	memset(hdr, 0, sizeof(*hdr));
 	hdr->code0 = htole32(ARM64_CODE0);
 	hdr->text_offset = htole64(image_entrypoint);
-	hdr->image_size = htole64(st.st_size + sizeof(*hdr));
+	hdr->image_size = htole64(dsize);
 	hdr->flags = htole32(flags);
 	hdr->magic = htole32(ARM64_MAGIC);