1 files changed, 3 insertions, 2 deletions
diff --git a/src/generic/problemresolver/incremental_expression.h b/src/generic/problemresolver/incremental_expression.h
index 4d77dcbb..2435f55d 100644
--- a/src/generic/problemresolver/incremental_expression.h
+++ b/src/generic/problemresolver/incremental_expression.h
@@ -192,9 +192,10 @@ public:
   // Add a weak reference to the given expression; its
   // child_modified() routine will be invoked when this child's value
   // changes.
-  void add_parent(const cwidget::util::ref_ptr<expression_container<T> > &parent)
+  void add_parent(expression_container<T> *parent)
   {
-    parents.push_back(parent);
+    if(parent != NULL)
+      parents.push_back(parent);
   }
 
   virtual T get_value() = 0;