diff --git a/README.md b/README.md
index 818eee8f..c6a547d3 100755
--- a/README.md
+++ b/README.md
@@ -245,6 +245,9 @@ Usage: digiarch extract [OPTIONS] [QUERY]
   To see the which files will be unpacked (but not their contents) without
   unpacking them, use the --dry-run option.
 
+  Extracted filenames longer than 20 characters will be trimmed and partially
+  prefixed with a unique hash based on the original name.
+
   Use the QUERY argument to specify which files should be unpacked. For
   details on the QUERY argument, see the edit command.