diff --git a/ExprNode.cc b/ExprNode.cc
index 7bb79e13996e7b00c1acf0dc792313966fb5fb77..959074d7de07cad44fbf2cbf71c01c7338107a53 100644
--- a/ExprNode.cc
+++ b/ExprNode.cc
@@ -2770,7 +2770,7 @@ UnaryOpNode::substituteAdl() const
     }
 
   expr_t arg1subst = arg->substituteAdl();
-  expr_t retval;
+  expr_t retval = NULL;
   ostringstream inttostr;
   if (adl_param_lag >= 0)
     {