diff --git a/include/class.forms.php b/include/class.forms.php
index 9fec2ec7d207117dea377711a7a148c30f94f01a..6618220058e7be217ee3526e1359651d8dd7de80 100644
--- a/include/class.forms.php
+++ b/include/class.forms.php
@@ -2689,7 +2689,7 @@ class FileUploadField extends FormField {
         ) {
             $this->attachments = GenericAttachments::forIdAndType(
                 // Combine the field and entry ids to make the key
-                sprintf('%u', crc32('E'.$this->get('id').$e->get('id'))),
+                sprintf('%u', abs(crc32('E'.$this->get('id').$e->get('id')))),
                 'E');
         }
         return $this->attachments ?: array();