diff --git a/README.md b/README.md
index 7f52b06..977c01f 100644
--- a/README.md
+++ b/README.md
@@ -45,7 +45,7 @@
 snapshots should be generated, the repository will be implicitly
 initialized to do so when generating keys.
 
-#### `tuf gen-key <role>`
+#### `tuf gen-key [--expires=<days>] <role>`
 
 Prompts the user for an encryption passphrase (unless the
 `--insecure-plaintext` flag is set), then generates a new signing key and