diff --git a/modules/views_rss_core/views_rss_core.inc b/modules/views_rss_core/views_rss_core.inc
index 8968963..ecb5f4f 100644
--- a/modules/views_rss_core/views_rss_core.inc
+++ b/modules/views_rss_core/views_rss_core.inc
@@ -310,15 +310,18 @@ function views_rss_core_preprocess_item_enclosure(&$variables) {
 
         // If the derivative doesn't exist yet, we won't be able to get its size
         // to add it to the 'length' attribute, so we need to create it first.
+        $check_file_size = TRUE;
         if (!file_exists($image_style_uri)) {
-          $image_style->createDerivative($image_uri, $image_style_uri);
+          $check_file_size = $image_style->createDerivative($image_uri, $image_style_uri);
         }
 
         $element['attributes'] = [
           'url' => $image_style->buildUrl($image_uri),
-          'length' => filesize($image_style_uri),
           'type' => $file->getMimeType(),
         ];
+        if ($check_file_size) {
+          $element['attributes']['length'] = filesize($image_style_uri);
+        }
       }
       // Normal image size.
       else {
diff --git a/modules/views_rss_media/views_rss_media.inc b/modules/views_rss_media/views_rss_media.inc
index 2a8fa48..b2434ee 100644
--- a/modules/views_rss_media/views_rss_media.inc
+++ b/modules/views_rss_media/views_rss_media.inc
@@ -40,13 +40,23 @@ function views_rss_media_preprocess_item_content(&$variables) {
       // Image style is defined, need to link to resized version.
       if ($image_style_name = $item['rendered']['#image_style']) {
         $image_style = ImageStyle::load($image_style_name);
-        $uri = $image_style->buildUri($file->getFileUri());
+        $image_style_uri = $image_style->buildUri($file->getFileUri());
         $url = $image_style->buildUrl($file->getFileUri());
+
+        // If the derivative doesn't exist yet, we won't be able to get its size
+        // to add it to the 'length' attribute, so we need to create it first.
+        $check_file_size = TRUE;
+        if (!file_exists($image_style_uri)) {
+          $check_file_size = $image_style->createDerivative($image_style_uri, $image_style_uri);
+        }
+
         $element['attributes'] = [
           'url' => $url,
-          'fileSize' => filesize(\Drupal::service('file_system')->realpath($uri)),
           'type' => $mime_type,
         ];
+        if ($check_file_size) {
+          $element['attributes']['fileSize'] = filesize($image_style_uri);
+        }
       }
       // Normal image size.
       else {