diff --git a/app/javascript/mastodon/features/compose/components/upload_button.js b/app/javascript/mastodon/features/compose/components/upload_button.js
index 70b28a2bae..2f38f5148d 100644
--- a/app/javascript/mastodon/features/compose/components/upload_button.js
+++ b/app/javascript/mastodon/features/compose/components/upload_button.js
@@ -7,7 +7,7 @@ import ImmutablePureComponent from 'react-immutable-pure-component';
 import ImmutablePropTypes from 'react-immutable-proptypes';
 
 const messages = defineMessages({
-  upload: { id: 'upload_button.label', defaultMessage: 'Add media' },
+  upload: { id: 'upload_button.label', defaultMessage: 'Add media (JPEG, PNG, GIF, WebM, MP4)' },
 });
 
 const makeMapStateToProps = () => {
diff --git a/app/javascript/mastodon/locales/en.json b/app/javascript/mastodon/locales/en.json
index 432c4f0b0a..3d8fdc0d79 100644
--- a/app/javascript/mastodon/locales/en.json
+++ b/app/javascript/mastodon/locales/en.json
@@ -297,7 +297,7 @@
   "trends.count_by_accounts": "{count} {rawCount, plural, one {person} other {people}} talking",
   "ui.beforeunload": "Your draft will be lost if you leave Mastodon.",
   "upload_area.title": "Drag & drop to upload",
-  "upload_button.label": "Add media",
+  "upload_button.label": "Add media (JPEG, PNG, GIF, WebM, MP4)",
   "upload_form.description": "Describe for the visually impaired",
   "upload_form.focus": "Crop",
   "upload_form.undo": "Delete",