diff --git a/client/css/post-upload.styl b/client/css/post-upload.styl
index 4da53a7..147df6b 100644
--- a/client/css/post-upload.styl
+++ b/client/css/post-upload.styl
@@ -22,6 +22,8 @@ $cancel-button-color = tomato
         .file-dropper
             font-size: 150%
             padding: 2em
+            small
+                font-size: 60%
 
     input[type=submit]
         margin-top: 1em
diff --git a/client/html/file_dropper.tpl b/client/html/file_dropper.tpl
index 9c66201..9e7715d 100644
--- a/client/html/file_dropper.tpl
+++ b/client/html/file_dropper.tpl
@@ -8,6 +8,10 @@
         <% } %>
         <br/>
         Or just click on this box.
+        <% if (ctx.extraText) { %>
+            <br/>
+            <small><%= ctx.extraText %></small>
+        <% } %>
     </label>
     <% if (ctx.allowUrls) { %>
         <input type='text' name='url' placeholder='Alternatively, paste an URL here.'/>
diff --git a/client/js/controls/file_dropper_control.js b/client/js/controls/file_dropper_control.js
index 113e7ac..7b3c120 100644
--- a/client/js/controls/file_dropper_control.js
+++ b/client/js/controls/file_dropper_control.js
@@ -11,8 +11,9 @@ class FileDropperControl extends events.EventTarget {
 
         this._options = options;
         const source = template({
-            allowMultiple: this._options.allowMultiple,
-            allowUrls: this._options.allowUrls,
+            extraText: options.extraText,
+            allowMultiple: options.allowMultiple,
+            allowUrls: options.allowUrls,
             id: 'file-' + Math.random().toString(36).substring(7),
         });
 
@@ -21,7 +22,7 @@ class FileDropperControl extends events.EventTarget {
         this._urlConfirmButtonNode = source.querySelector('button');
         this._fileInputNode = source.querySelector('input[type=file]');
         this._fileInputNode.style.display = 'none';
-        this._fileInputNode.multiple = this._options.allowMultiple || false;
+        this._fileInputNode.multiple = options.allowMultiple || false;
 
         this._counter = 0;
         this._dropperNode.addEventListener(
diff --git a/client/js/views/post_upload_view.js b/client/js/views/post_upload_view.js
index 144526b..f80135f 100644
--- a/client/js/views/post_upload_view.js
+++ b/client/js/views/post_upload_view.js
@@ -156,6 +156,8 @@ class PostUploadView extends events.EventTarget {
         this._contentFileDropper = new FileDropperControl(
             this._contentInputNode,
             {
+                extraText:
+                    'Allowed extensions: .jpg, .png, .gif, .webm, .mp4, .swf',
                 allowUrls: true,
                 allowMultiple: true,
                 lock: false,