diff --git a/README.md b/README.md
index 31e6a57..3185444 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,8 @@ Use `!tmdb movie {title} [y:{release year}]` to get movie detail based on the gi
 
 Use `!tmdb language {language}` to set your prefered language.
 
+Use `!tmdb poster_size [{size}]` to set your prefered poster size. With empty {size} all available sizes are listed.
+
 Use `!tmdb tvshow {title}` to get detail about a tv show based on the given title.
 
 ## Discussion
diff --git a/tmdb/tmdb.py b/tmdb/tmdb.py
index 385f17a..55e1565 100644
--- a/tmdb/tmdb.py
+++ b/tmdb/tmdb.py
@@ -65,7 +65,7 @@ class TmdbBot(Plugin):
         html = """<p>Use <b>!tmdb id movie {tmdb id}</b> to get movie detail for tmdb-id.</p>
                   <p>Use <b>!tmdb movie {title} [y:{release year}]</b> to get movie detail based on the given title.</p>
                   <p>Use <b>!tmdb language {language}</b> to set your prefered language.</p>
-                  <p>Use <b>!tmdb poster_size {size}</b> to set your prefered poster size. With empty {size} all available sizes are listed.</p>
+                  <p>Use <b>!tmdb poster_size [{size}]</b> to set your prefered poster size. With empty {size} all available sizes are listed.</p>
                   <p>Use <b>!tmdb tvshow {title}</b> to get detail about a tv show based on the given title.</p>"""
         content = TextMessageEventContent(
             msgtype=MessageType.TEXT, format=Format.HTML,