diff --git a/blocks/tag_flickr/block_tag_flickr.php b/blocks/tag_flickr/block_tag_flickr.php
index affb9dea587..30aec42ec7d 100644
--- a/blocks/tag_flickr/block_tag_flickr.php
+++ b/blocks/tag_flickr/block_tag_flickr.php
@@ -22,9 +22,12 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+defined('MOODLE_INTERNAL') || die();
 define('FLICKR_DEV_KEY', '4fddbdd7ff2376beec54d7f6afad425e');
 define('DEFAULT_NUMBER_OF_PHOTOS', 6);
 
+require_once("{$CFG->libdir}/flickrclient.php");
+
 class block_tag_flickr extends block_base {
 
     function init() {
@@ -102,7 +105,11 @@ class block_tag_flickr extends block_base {
 
             $response = $this->fetch_request($request);
 
-            $search = unserialize($response);
+            $search = @unserialize($response);
+            if ($search === false && $search != serialize(false)) {
+                // The response didn't appear to be anything serialized, exit...
+                return;
+            }
 
             foreach ($search['photoset']['photo'] as $p){
                 $p['owner'] = $search['photoset']['owner'];
@@ -123,7 +130,11 @@ class block_tag_flickr extends block_base {
 
             $response = $this->fetch_request($request);
 
-            $search = unserialize($response);
+            $search = @unserialize($response);
+            if ($search === false && $search != serialize(false)) {
+                // The response didn't appear to be anything serialized, exit...
+                return;
+            }
             $photos = array_values($search['photos']['photo']);
         }
 
@@ -147,6 +158,10 @@ class block_tag_flickr extends block_base {
 
     function fetch_request($request){
         $c =  new curl(array('cache' => true, 'module_cache'=> 'tag_flickr'));
+        // Set custom user agent as Flickr blocks our "MoodleBot" agent string.
+        $c->setopt([
+            'CURLOPT_USERAGENT' => flickr_client::user_agent(),
+        ]);
 
         $response = $c->get($request);