diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml b/documentation/dev-manual/dev-manual-common-tasks.xml
index 65a6b6fe33..2c949908c5 100644
--- a/documentation/dev-manual/dev-manual-common-tasks.xml
+++ b/documentation/dev-manual/dev-manual-common-tasks.xml
@@ -5166,7 +5166,7 @@ the details.
                 </literallayout>
                 or
                 <literallayout class='monospaced'>
-     EXTRA_IMAGE_FEATURES = "read-only-rootfs"
+     EXTRA_IMAGE_FEATURES += "read-only-rootfs"
                 </literallayout>
             </para>