diff --git a/letsencrypt/cli.py b/letsencrypt/cli.py
index 8bd15d404..61b367a9c 100644
--- a/letsencrypt/cli.py
+++ b/letsencrypt/cli.py
@@ -861,7 +861,7 @@ def _create_subparsers(helpful):
                 "--csr", type=read_file,
                 help="Path to a Certificate Signing Request (CSR) in DER"
                 " format; note that the .csr file *must* contain a Subject"
-                " Alternative Name field for each domain you want certified")
+                " Alternative Name field for each domain you want certified.")
     helpful.add("rollback",
                 "--checkpoints", type=int, metavar="N",
                 default=flag_default("rollback_checkpoints"),