diff --git a/product/ERP5/Document/Delivery.py b/product/ERP5/Document/Delivery.py
index fd42fb67c5105d2c03c99dbaf373c4dbbdcf77fc..d5c029218b1e0abb9e687ef73623809f1c7f9815 100755
--- a/product/ERP5/Document/Delivery.py
+++ b/product/ERP5/Document/Delivery.py
@@ -499,6 +499,9 @@ une liste de mouvements..."""
         emit targetUnreachable !
       """
       from DateTime import DateTime
+      if self.getStartDate() is None or self.getTargetStartDate() is None \
+               or self.getStopDate() is None or self.getTargetStopDate() is None:
+        return 1
       # This is uggly but required due to python2.2/2.3 Zope 2.6/2.7 inconsistency in _millis calculation
       if self.getStartDate().Date() != self.getTargetStartDate().Date()  or \
          self.getStopDate().Date() != self.getTargetStopDate().Date():
diff --git a/product/ERP5/Document/Movement.py b/product/ERP5/Document/Movement.py
index 2be026362e9acb2bd20101f6e20ca50b9cff1ed6..9a0244356cc3d8783f70b3de7ef60ae28db9b67d 100755
--- a/product/ERP5/Document/Movement.py
+++ b/product/ERP5/Document/Movement.py
@@ -382,6 +382,9 @@ a service in a public administration)."""
 
       emit targetUnreachable !
     """
+    if self.getStartDate() is None or self.getTargetStartDate() is None \
+            or self.getStopDate() is None or self.getTargetStopDate() is None:
+      return 1
     # This is uggly but required due to python2.2/2.3 Zope 2.6/2.7 inconsistency in _millis calculation
     return self.getQuantity() != self.getTargetQuantity() or \
            self.getStartDate().Date() != self.getTargetStartDate().Date() or \