diff --git a/src/Entity/AttachmentThumbnail.php b/src/Entity/AttachmentThumbnail.php
index 24b17d2c95..f0798e294e 100644
--- a/src/Entity/AttachmentThumbnail.php
+++ b/src/Entity/AttachmentThumbnail.php
@@ -170,6 +170,7 @@ class AttachmentThumbnail extends Entity
                 });
         } catch (NotFoundException $e) {
             $thumbnail = self::create(['attachment_id' => $attachment->getId()]);
+            $event_map = [];
             Event::handle('ResizerAvailable', [&$event_map]);
             $mimetype   = $attachment->getMimetype();
             $major_mime = GSFile::mimetypeMajor($mimetype);