diff --git a/mayan/apps/document_signatures/models.py b/mayan/apps/document_signatures/models.py
index 4e584b381c..ead15e53d0 100644
--- a/mayan/apps/document_signatures/models.py
+++ b/mayan/apps/document_signatures/models.py
@@ -11,7 +11,6 @@ from documents.runtime import storage_backend
 
 from .managers import DocumentVersionSignatureManager
 
-UUID_FUNCTION = lambda x: unicode(uuid.uuid4())
 logger = logging.getLogger(__name__)
 
 
@@ -20,7 +19,7 @@ class DocumentVersionSignature(models.Model):
     Model that describes a document version signature properties
     """
     document_version = models.ForeignKey(DocumentVersion, verbose_name=_(u'Document version'), editable=False)
-    signature_file = models.FileField(blank=True, null=True, upload_to=lambda instance, filename: UUID_FUNCTION(), storage=storage_backend, verbose_name=_(u'Signature file'), editable=False)
+    signature_file = models.FileField(blank=True, null=True, upload_to=lambda instance, filename: unicode(uuid.uuid4()), storage=storage_backend, verbose_name=_(u'Signature file'), editable=False)
     has_embedded_signature = models.BooleanField(default=False, verbose_name=_(u'Has embedded signature'), editable=False)
 
     objects = DocumentVersionSignatureManager()