diff --git a/lib/filelib.php b/lib/filelib.php
index eebedb09b56..ea0e4fcd8d6 100644
--- a/lib/filelib.php
+++ b/lib/filelib.php
@@ -1984,6 +1984,23 @@ function send_stored_file($stored_file, $lifetime=86400 , $filter=0, $forcedownl
         $dontdie = true;
     }
 
+    if (!empty($options['preview'])) {
+        // replace the file with its preview
+        $fs = get_file_storage();
+        $stored_file = $fs->get_file_preview($stored_file, $options['preview']);
+        if (!$stored_file) {
+            // unable to create a preview of the file
+            send_header_404();
+            die();
+        } else {
+            // preview images have fixed cache lifetime and they ignore forced download
+            // (they are generated by GD and therefore they are considered reasonably safe).
+            $lifetime = DAYSECS;
+            $filter = 0;
+            $forcedownload = false;
+        }
+    }
+
     if (!$stored_file or $stored_file->is_directory()) {
         // nothing to serve
         if ($dontdie) {