diff --git a/changelog.d/12715.doc b/changelog.d/12715.doc
new file mode 100644
index 0000000000..150d78c3f6
--- /dev/null
+++ b/changelog.d/12715.doc
@@ -0,0 +1 @@
+Fix a typo in the Media Admin API documentation.
diff --git a/docs/admin_api/media_admin_api.md b/docs/admin_api/media_admin_api.md
index 96b3668f2a..d57c5aedae 100644
--- a/docs/admin_api/media_admin_api.md
+++ b/docs/admin_api/media_admin_api.md
@@ -289,7 +289,7 @@ POST /_synapse/admin/v1/purge_media_cache?before_ts=<unix_timestamp_in_ms>
 
 URL Parameters
 
-* `unix_timestamp_in_ms`: string representing a positive integer - Unix timestamp in milliseconds.
+* `before_ts`: string representing a positive integer - Unix timestamp in milliseconds.
 All cached media that was last accessed before this timestamp will be removed.
 
 Response: