diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 5b0e593c3d..7539136734 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -6400,6 +6400,11 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
                     <literallayout class='monospaced'>
      SDKMACHINE ?= "i686"
                     </literallayout>
+                    <note>
+                        You cannot set the <filename>SDKMACHINE</filename>
+                        variable in your distribution configuration file.
+                        If you do, the configuration will not take affect.
+                    </note>
                 </para>
             </glossdef>
         </glossentry>