diff --git a/README.rst b/README.rst
index 72b1b07..933c433 100644
--- a/README.rst
+++ b/README.rst
@@ -184,7 +184,7 @@ message *about starting the server*::
                           use "auto", which chooses one of paste, cherrypy, twisted, or wsgiref.
     -o, --overwrite       Allow overwriting existing package files during upload.
     --welcome HTML_FILE   Use the contents of HTML_FILE as a custom welcome message on the home page.
-    --cache-control AGE   Add "Cache-Control: max-age=AGE" header to package downloads. Pip 6+ requires this for caching.
+    --cache-control AGE   Add "Cache-Control: max-age=AGE" header to package downloads. Pip 6+ requires this for caching. AGE is specified in seconds.
     --log-req-frmt FORMAT
                           A format-string selecting Http-Request properties to log; set to '%s' to see them all.
     --log-res-frmt FORMAT
diff --git a/pypiserver/config.py b/pypiserver/config.py
index f92dfea..1bd102a 100644
--- a/pypiserver/config.py
+++ b/pypiserver/config.py
@@ -453,6 +453,7 @@ def get_parser() -> argparse.ArgumentParser:
         help=(
             'Add "Cache-Control: max-age=AGE" header to package downloads. '
             "Pip 6+ requires this for caching."
+            "AGE is specified in seconds."
         ),
     )
     run_parser.add_argument(