diff --git a/src/simplugin.cpp b/src/simplugin.cpp
--- a/src/simplugin.cpp
+++ b/src/simplugin.cpp
@@ -20,6 +20,7 @@
  */
 
 #include <string>
+#include <QString>
 #include "simplugin.h"
 
 static const std::string _module_id("$Id$");
@@ -34,4 +35,6 @@ void SimPluginInterface::SetCellsStaticD
   CellBase::static_data_members = cells_static_data_members_of_main;
 }
 
+QString SimPluginInterface::DefaultLeafML(void) { return QString(); }
+
 /* finis */