diff --git a/src/gui/gtk-lumiera.hpp b/src/gui/gtk-lumiera.hpp
index 41b355d80..d3c59d7ba 100644
--- a/src/gui/gtk-lumiera.hpp
+++ b/src/gui/gtk-lumiera.hpp
@@ -114,6 +114,11 @@ GtkLumiera& application();
  */
 namespace dialogs {}
 
+/**
+ * The namespace of data model classes.
+ */
+namespace model {}
+
 /**
  * The namespace of all video output implementations.
  */