diff --git a/include/wx/layout.h b/include/wx/layout.h
index 388398b9e1..8fb28aa42e 100644
--- a/include/wx/layout.h
+++ b/include/wx/layout.h
@@ -149,6 +149,8 @@ protected:
     int percent;
     wxEdge otherEdge;
     bool done;
+
+    DECLARE_DYNAMIC_CLASS(wxIndividualLayoutConstraint)
 };
 
 // ----------------------------------------------------------------------------