diff --git a/src/expression2/DDefineExpr.cpp b/src/expression2/DDefineExpr.cpp
index 8afb90fe..83ee9188 100644
--- a/src/expression2/DDefineExpr.cpp
+++ b/src/expression2/DDefineExpr.cpp
@@ -85,7 +85,8 @@ namespace xo {
                 return ppii.pps()->pretty_struct
                            (ppii,
                             "DDefineExpr",
-                            refrtag("lhs", lhs));
+                            refrtag("lhs", lhs),
+                            refrtag("rhs", "nullptr"));
             }
         }