diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 0ee36d09c0..df903a4b4d 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -9234,6 +9234,20 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
             </glossdef>
         </glossentry>
 
+        <glossentry id='var-SDK_OS'><glossterm><imagedata fileref="figures/define-generic.png" />SDK_OS</glossterm>
+            <info>
+                SDK_OS[doc] = "The operating system for which the SDK will be built."
+            </info>
+            <glossdef>
+                <para>
+                    Specifies the operating system for which the SDK
+                    will be built.
+                    The default value is the value of
+                    <link linkend='var-BUILD_OS'><filename>BUILD_OS</filename></link>.
+                </para>
+            </glossdef>
+        </glossentry>
+
         <glossentry id='var-SDK_OUTPUT'><glossterm><imagedata fileref="figures/define-generic.png" />SDK_OUTPUT</glossterm>
             <info>
                 SDK_OUTPUT[doc] = "The location used by the OpenEmbedded build system when creating SDK output."