diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index 8af233004f..7ae61ad0ff 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -7925,6 +7925,11 @@ system and gives an overview of their function and contents.
       image), compared to just using the :ref:`ref-classes-create-spdx` class
       with no option.
 
+   :term:`SPDX_NAMESPACE_PREFIX`
+      This option could be used in order to change the prefix of ``spdxDocument``
+      and the prefix of ``documentNamespace``. It is set by default to
+      ``http://spdx.org/spdxdoc``.
+
    :term:`SPDX_PRETTY`
       This option makes the SPDX output more human-readable, using
       identation and newlines, instead of the default output in a