diff --git a/etc/build.props b/etc/build.props
index 144929b..9ba4817 100644
--- a/etc/build.props
+++ b/etc/build.props
@@ -5,7 +5,9 @@ requirements = \
   env:ISABELLE_SCALA_JAR
 sources = \
   Isabelle_DOF/scala/dof.scala \
+  Isabelle_DOF/scala/dof_document_build.scala \
   scala/dof_mkroot.scala \
   scala/dof_tools.scala
 services = \
-  isabelle.dof.DOF_Tools
+  isabelle.dof.DOF_Tools \
+  isabelle.dof.DOF_Document_Build$Engine