diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 88539ae5ec..4c4fc22717 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -6409,6 +6409,27 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
             </glossdef>
         </glossentry>
 
+        <glossentry id='var-KERNEL_CLASSES'><glossterm>KERNEL_CLASSES</glossterm>
+            <info>
+                KERNEL_CLASSES[doc] = "A list of classes defining kernel image types that kernel class should inherit."
+            </info>
+            <glossdef>
+                <para role="glossdeffirst">
+<!--                <para role="glossdeffirst"><imagedata fileref="figures/define-generic.png" /> -->
+                    A list of classes defining kernel image types that the
+                    <link linkend='ref-classes-kernel'><filename>kernel</filename></link>
+                    class should inherit.
+                    You typically append this variable to enable extended image
+                    types.
+                    An example is the "kernel-fitimage", which enables
+                    fitImage support and resides in
+                    <filename>meta/classes/kernel-fitimage.bbclass</filename>.
+                    You can register custom kernel image types with the
+                    <filename>kernel</filename> class using this variable.
+                </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."