diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index a36c4c6df962..c561aae6563a 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -4275,7 +4275,7 @@ system and gives an overview of their function and contents.
       To use the variable, set it in the append file for your kernel recipe
       using the following form::
 
-         KBUILD_DEFCONFIG_KMACHINE ?= defconfig_file
+         KBUILD_DEFCONFIG_KMACHINE ?= "defconfig_file"
 
       Here is an example from a "raspberrypi2" :term:`KMACHINE` build that uses
       a ``defconfig`` file named "bcm2709_defconfig"::