diff --git a/product/ERP5SyncML/Signature.py b/product/ERP5SyncML/Signature.py
index de636233a26f50162ed07f4b96887abfa44cd1bd..5a4d1d4adca29b18175e06ccd03fdcbdb7267eae 100644
--- a/product/ERP5SyncML/Signature.py
+++ b/product/ERP5SyncML/Signature.py
@@ -390,7 +390,7 @@ class Signature(Folder, SyncCode, File):
     chunk.append(self.partial_xml.data)
     size = chunk[0].count('\n')
     current = next = self.partial_xml.next
-    while size < size_lines:
+    while size < size_lines and next is not None:
       current = next
       size += current.data.count('\n')
       chunk.append(current.data)