diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml b/documentation/dev-manual/dev-manual-common-tasks.xml
index 7138f5dca6..8d251a0125 100644
--- a/documentation/dev-manual/dev-manual-common-tasks.xml
+++ b/documentation/dev-manual/dev-manual-common-tasks.xml
@@ -4435,7 +4435,7 @@
                 </literallayout>
                 or
                 <literallayout class='monospaced'>
-     EXTRA_IMAGE_FEATURES = "read-only-rootfs"
+     EXTRA_IMAGE_FEATURES += "read-only-rootfs"
                 </literallayout>
             </para>