diff --git a/src/Plugin/Field/FieldType/BgImgItem.php b/src/Plugin/Field/FieldType/BgImgItem.php
index 8e9f4d1604b9b903a9a4ccc5f5f9bd21f0ee61e5..d0c50ec9cd0ae7fd7cdac31b0a2ab9048ecaec79 100644
--- a/src/Plugin/Field/FieldType/BgImgItem.php
+++ b/src/Plugin/Field/FieldType/BgImgItem.php
@@ -245,6 +245,6 @@ class BgImgItem extends ImageItem {
 
     // Handle the custom file extensions setting before saving.
     $extensions = preg_split('/[\s,]+/', $this->getSetting('file_extensions'));
-    $this->setSetting('file_extensions', implode(' ', array_filter($extensions)));
+    $this->file_extensions = implode(' ', array_filter($extensions));
   }
 }