diff --git a/product/ERP5Type/BTreeData.py b/product/ERP5Type/BTreeData.py
index 642d70d65e7d525214c6ce61762930ad06ce29be..49125be72772cf5ea42825880ffdb03e06864613 100644
--- a/product/ERP5Type/BTreeData.py
+++ b/product/ERP5Type/BTreeData.py
@@ -11,6 +11,10 @@ class PersistentString(Persistent):
     def __str__(self):
         return self.value
 
+    # Save place when storing this data in zodb
+    __getstate__ = __str__
+    __setstate__ = __init__
+
 negative_offset_error = ValueError('Negative offset')
 
 class BTreeData(Persistent):