diff --git a/build/mk-bootimg.sh b/build/mk-bootimg.sh
index 642150f..e23cd76 100755
--- a/build/mk-bootimg.sh
+++ b/build/mk-bootimg.sh
@@ -130,8 +130,41 @@ cat > "$WORKDIR/boot.its" <<'ITS'
 };
 ITS
 
-echo "== FIT (external data, -E -p 0x800)"
-( cd "$WORKDIR" && mkimage -f boot.its -E -p 0x800 boot.img >/dev/null )
+#   - SUB-IMAGE ALIGNMENT (`-B 0x800`). `-p` only places the FIRST payload; the
+#     rest are packed contiguously, and U-Boot reads each one by dividing its
+#     data-position by the 512-byte block size with a TRUNCATING divide. A
+#     payload that is not block-aligned is therefore read from the wrong offset:
+#     the RESC loader's sha256 fails and logo.bmp silently does not load
+#     (observed 2026-09-01, flare-edge 9387cff).
+#
+#     MEASURED, both directions. Without -B, this script produced kernel at
+#     0x9A94 (data-position % 512 = 148) -- misaligned, exactly the failing
+#     shape. The vendor images that actually boot this board are aligned to
+#     0x800, not merely to 512: boot.img has fdt/kernel/resource at 0x800,
+#     0x12800, 0x3A7800 and recovery.img at 0x800, 0x12800, 0x3F8800 -- every
+#     one a multiple of 2048.
+#
+#     9387cff recorded `-B 0x200` from that failure. It is right but weaker than
+#     it needed to be: it was inferred from noticing the proven image was
+#     "512-aligned" without checking for a larger factor. 0x800 satisfies
+#     everything 0x200 does (every 0x800 multiple is a 0x200 multiple) and
+#     additionally reproduces the vendor layout exactly, for at most 2 KiB of
+#     padding. When the two disagree, match the image that is known to boot.
+echo "== FIT (external data, -E -p 0x800 -B 0x800)"
+( cd "$WORKDIR" && mkimage -f boot.its -E -p 0x800 -B 0x800 boot.img >/dev/null )
+
+# Every payload must land on a 0x800 boundary. This is the check that would have
+# caught the unaligned build before it reached a panel, so it runs on every
+# build rather than living in a separate tool nobody remembers to invoke.
+for _n in fdt kernel resource; do
+    _pos="$(fdtget -t u "$WORKDIR/boot.img" "/images/$_n" data-position 2>/dev/null || true)"
+    [ -n "$_pos" ] || continue
+    if [ $(( _pos % 2048 )) -ne 0 ]; then
+        echo "FATAL: /images/$_n data-position $_pos is not 0x800-aligned;" >&2
+        echo "       U-Boot's block divide would read it from the wrong offset" >&2
+        exit 1
+    fi
+done
 
 # A FIT whose metadata swelled to the size of the whole image is an
 # embedded-data build, which this U-Boot rejects. Catch it here rather than on