diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index e70445762f..fac6d9046b 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -6276,6 +6276,57 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
             </glossdef>
         </glossentry>
 
+        <glossentry id='var-KBUILD_DEFCONFIG'><glossterm>KBUILD_DEFCONFIG</glossterm>
+            <info>
+                KBUILD_DEFCONFIG[doc] = "Specifies an "in-tree" kernel configuration file for use during a kernel build."
+            </info>
+            <glossdef>
+                <para role="glossdeffirst">
+<!--                <para role="glossdeffirst"><imagedata fileref="figures/define-generic.png" /> -->
+                    When used with the
+                    <link linkend='ref-classes-kernel-yocto'><filename>kernel-yocto</filename></link>
+                    class, specifies an "in-tree" kernel configuration file
+                    for use during a kernel build.
+                </para>
+
+                <para>
+                    Typically, when using a <filename>defconfig</filename> to
+                    configure a kernel during a build, you place the
+                    file in your layer in the same manner as you would
+                    patch files and configuration fragment files (i.e.
+                    "out-of-tree").
+                    However, if you want to use a <filename>defconfig</filename>
+                    file that is part of the kernel tree (i.e. "in-tree"),
+                    you can use the
+                    <filename>KBUILD_DEFCONFIG</filename> variable to point
+                    to the <filename>defconfig</filename> file.
+                </para>
+
+                <para>
+                    To use the variable, set it in the append file for your
+                    kernel recipe using the following form:
+                    <literallayout class='monospaced'>
+     KBUILD_DEFCONFIG_<link linkend='var-KMACHINE'>KMACHINE</link> ?= <replaceable>defconfig_file</replaceable>
+                    </literallayout>
+                    Here is an example from a "raspberrypi2"
+                    <filename>KMACHINE</filename> build that uses a
+                    <filename>defconfig</filename> file named
+                    "bcm2709_defconfig":
+                    <literallayout class='monospaced'>
+     KBUILD_DEFCONFIG_raspberrypi2 = "bcm2709_defconfig"
+                    </literallayout>
+                    As an alternative, you can use the following within your
+                    append file:
+                    <literallayout class='monospaced'>
+     KBUILD_DEFCONFIG_pn-linux-yocto ?= <replaceable>defconfig_file</replaceable>
+                    </literallayout>
+                    For more information on how to use the
+                    <filename>KBUILD_DEFCONFIG</filename> variable, see the
+                    "TBD" section.
+                </para>
+            </glossdef>
+        </glossentry>
+
         <glossentry id='var-KERNEL_EXTRA_ARGS'><glossterm>KERNEL_EXTRA_ARGS</glossterm>
             <info>
                 KERNEL_EXTRA_ARGS[doc] = "Specifies additional make command-line arguments the OpenEmbedded build system passes on when compiling the kernel."