diff --git a/product/ERP5/PropertySheet/SolverType.py b/product/ERP5/PropertySheet/SolverType.py
index 2115660a33354572dab1342d8fcc3931b90934e5..cbb0d6cf8569b2ed7363f5c97c28e87ca8ce7b58 100644
--- a/product/ERP5/PropertySheet/SolverType.py
+++ b/product/ERP5/PropertySheet/SolverType.py
@@ -32,7 +32,8 @@ class SolverType:
 
     _properties = (
         { 'id':         'tested_property',
-          'type':       'string',
+          'type':       'lines',
+          'default'     : (),
           'mode':       'w',
           'label':      'Property to be solved'
          },