diff --git a/modules/purchase/doc/design.rst b/modules/purchase/doc/design.rst
index 138eb1efd8..dc38c6f808 100644
--- a/modules/purchase/doc/design.rst
+++ b/modules/purchase/doc/design.rst
@@ -106,6 +106,11 @@ Some fields on a draft purchase become read-only when lines are added to it.
 The *Modify Header* wizard allows the values in these fields to be safely
 updated.
 
+.. note::
+
+   When the header is modified, some of the properties of the lines will be
+   recalculated.
+
 .. _wizard-purchase.return_purchase:
 
 Return Purchase
diff --git a/modules/sale/doc/design.rst b/modules/sale/doc/design.rst
index 39e28b6dd4..295641c529 100644
--- a/modules/sale/doc/design.rst
+++ b/modules/sale/doc/design.rst
@@ -110,6 +110,11 @@ Some fields on a draft sale become read-only when lines are added to it.
 The *Modify Header* wizard allows the values in these fields to be safely
 updated.
 
+.. note::
+
+   When the header is modified, some of the properties of the lines will be
+   recalculated.
+
 .. _wizard-sale.return_sale:
 
 Return Sale