diff --git a/pureboot/README.md b/pureboot/README.md
index 791391b..ff5ee7d 100644
--- a/pureboot/README.md
+++ b/pureboot/README.md
@@ -124,7 +124,9 @@ the loader; an erase runs top-down for the same reason.
 
 `pureboot.py --update-loader new_pureboot.bin` replaces the resident loader
 with any pureboot build — a re-timed window, a newer protocol — using the
-loader itself as its own staging loader:
+loader itself as its own staging loader. The image is the loader's own 512
+bytes as a raw binary, or the Intel HEX the build emits beside it, which
+links the loader at its base inside an otherwise blank flash image:
 
 1. The staging slot `[base−512, base)` is saved to a host-side state file
    (on the 1 KB tiny13A that is the whole application, vectors included).
diff --git a/pureboot/pureboot.py b/pureboot/pureboot.py
index b3540ec..c76e886 100644
--- a/pureboot/pureboot.py
+++ b/pureboot/pureboot.py
@@ -514,6 +514,20 @@ def image_info(image):
     return Info(image[at : at + 12]) if 0 <= at <= len(image) - 12 else None
 
 
+def loader_image(path):
+    """A loader update image, as the slot's own content. A raw binary is that
+    already; an Intel HEX links the loader at its base inside an otherwise
+    blank flash image, and load_image() anchors every image at zero, so the
+    blank below the base is dropped here. The base comes from the image's own
+    info block rather than the device's, so an image built for somewhere else
+    survives intact and the preflight can say so."""
+    image = load_image(path)
+    embedded = image_info(image)
+    if embedded and len(image) > embedded.base:
+        image = image[embedded.base :]
+    return image
+
+
 def staging_content(image, info):
     """The 512-byte staging-slot content: the image, padding, and — on
     chips whose hand-over jumps through the word below the resident loader —
@@ -643,7 +657,7 @@ def op_update_loader(loader, wait, path, state_path, fuse_bytes):
     actual flash state, so a re-run after any interruption resumes; the
     state file carries the bytes the staging slot held."""
     info = loader.info
-    image = load_image(path)
+    image = loader_image(path)
     for warning in update_preflight(image, info, fuse_bytes):
         print(f"note: {warning}")
     staged = staging_content(image, info)