diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index ee5cbc2d65..eed3c47e1a 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -3337,6 +3337,32 @@
+ EXTERNAL_KERNEL_TOOLS
+
+ EXTERNAL_KERNEL_TOOLS[doc] = "Indicates kernel tools are external to the source tree."
+
+
+
+
+ When set, the EXTERNAL_KERNEL_TOOLS
+ variable indicates that these tools are not in the
+ source tree.
+
+
+
+ When kernel tools are available in the tree, they are
+ preferred over any externally installed tools.
+ Setting the EXTERNAL_KERNEL_TOOLS
+ variable tells the OpenEmbedded build system to prefer
+ the installed external tools.
+ See the
+ kernel-yocto
+ class in meta/classes to see how
+ the variable is used.
+
+
+
+
EXTERNALSRC
EXTERNALSRC[doc] = "If externalsrc.bbclass is inherited, this variable points to the source tree, which is outside of the OpenEmbedded build system."