diff --git a/README.md b/README.md
index 022c95f..aac455e 100644
--- a/README.md
+++ b/README.md
@@ -63,6 +63,8 @@ status and refs are printed to stderr.
   `TYPE_TAG_PEL_PROGRAM_DAG_1` (`0x00000101`).
 - `amduat-pel-run` reports `result_ref`, `trace_ref`, and `output_ref[N]`
   when not using `--output-raw`.
+- The filesystem ASL store layout expects digests at least 2 bytes long
+  (two directory levels). Experimental shorter digests need a different store.
 
 ## PEL reference