diff --git a/blocks/tag_flickr/block_tag_flickr.php b/blocks/tag_flickr/block_tag_flickr.php
index 30aec42ec7d..df1efb42a9d 100644
--- a/blocks/tag_flickr/block_tag_flickr.php
+++ b/blocks/tag_flickr/block_tag_flickr.php
@@ -101,13 +101,14 @@ class block_tag_flickr extends block_base {
             $request .= '&api_key='.FLICKR_DEV_KEY;
             $request .= '&photoset_id='.$this->config->photoset;
             $request .= '&per_page='.$numberofphotos;
-            $request .= '&format=php_serial';
+            $request .= '&format=json';
+            // We need to add nojsoncallback=? here, otherwise, Flickr will return the jsonFlickrApi object.
+            $request .= '&nojsoncallback=?';
 
             $response = $this->fetch_request($request);
-
-            $search = @unserialize($response);
-            if ($search === false && $search != serialize(false)) {
-                // The response didn't appear to be anything serialized, exit...
+            $search = @json_decode($response, true);
+            if (!is_array($search) || json_last_error() !== JSON_ERROR_NONE) {
+                // The response didn't appear to be in correct format.
                 return;
             }
 
@@ -126,13 +127,14 @@ class block_tag_flickr extends block_base {
             $request .= '&tags='.$tagscsv;
             $request .= '&per_page='.$numberofphotos;
             $request .= '&sort='.$sortby;
-            $request .= '&format=php_serial';
+            $request .= '&format=json';
+            // We need to add nojsoncallback=? here, otherwise, Flickr will return the jsonFlickrApi object.
+            $request .= '&nojsoncallback=?';
 
             $response = $this->fetch_request($request);
-
-            $search = @unserialize($response);
-            if ($search === false && $search != serialize(false)) {
-                // The response didn't appear to be anything serialized, exit...
+            $search = @json_decode($response, true);
+            if (!is_array($search) || json_last_error() !== JSON_ERROR_NONE) {
+                // The response didn't appear to be in correct format.
                 return;
             }
             $photos = array_values($search['photos']['photo']);