diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index d559899c6..c18bc7ba4 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -4166,6 +4166,11 @@ 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's value is defined by the ``--overhead-factor`` option, and
+      not by :term:`IMAGE_OVERHEAD_FACTOR`. See the
+      ":doc:`/ref-manual/kickstart`" chapter 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