diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index ef64bcad49..59b71a4ef7 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -4079,6 +4079,12 @@ system and gives an overview of their function and contents.
       added to the image by using the :term:`IMAGE_ROOTFS_EXTRA_SPACE`
       variable.
 
+      When using Wic tool, beware that a second overhead factor is also applied.
+      This overhead value is defined by the ``--overhead-factor`` option, which
+      defaults to "1.3" when omitted. See the
+      :ref:`ref-manual/kickstart:command: part or partition` chapter in
+      :doc:`/ref-manual/kickstart` for details.
+
    :term:`IMAGE_PKGTYPE`
       Defines the package type (i.e. DEB, RPM or IPK) used by the
       OpenEmbedded build system. The variable is defined appropriately by