diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 72ec7db3d7..698b0082ae 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -9311,13 +9311,23 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
 
         <glossentry id='var-SDK_SYS'><glossterm><imagedata fileref="figures/define-generic.png" />SDK_SYS</glossterm>
             <info>
-                SDK_SYS[doc] = "Specifies the SDK system, including the architecture and the operating system, for which the build is occurring in the context of the current recipe."
+                SDK_SYS[doc] = "Specifies the system, including the architecture and the operating system, for which the SDK will be built."
             </info>
             <glossdef>
                 <para>
-                    Specifies the SDK system, including the architecture and
-                    the operating system, for which the build is occurring
-                    in the context of the current recipe.
+                    Specifies the system, including the architecture and the
+                    operating system, for which the SDK will be built.
+                </para>
+
+                <para>
+                    The OpenEmbedded build system automatically sets this
+                    variable based on
+                    <link linkend='var-SDK_ARCH'><filename>SDK_ARCH</filename></link>,
+                    <link linkend='var-SDK_VENDOR'><filename>SDK_VENDOR</filename></link>,
+                    and
+                    <link linkend='var-SDK_OS'><filename>SDK_OS</filename></link>.
+                    You do not need to set the <filename>SDK_SYS</filename>
+                    variable yourself.
                 </para>
             </glossdef>
         </glossentry>