diff --git a/vhdlpp/expression.cc b/vhdlpp/expression.cc
index 7bb97642f..b8c1113d4 100644
--- a/vhdlpp/expression.cc
+++ b/vhdlpp/expression.cc
@@ -894,3 +894,11 @@ ExpDelay::~ExpDelay()
     delete expr_;
     delete delay_;
 }
+
+void ExpDelay::visit(ExprVisitor& func)
+{
+    expr_->visit(func);
+    delay_->visit(func);
+
+    func(this);
+}
diff --git a/vhdlpp/expression.h b/vhdlpp/expression.h
index 8dc5d1126..b09b5fdd2 100644
--- a/vhdlpp/expression.h
+++ b/vhdlpp/expression.h
@@ -992,6 +992,7 @@ public:
     void write_to_stream(std::ostream&) const;
     int emit(ostream&out, Entity*ent, ScopeBase*scope) const;
     void dump(ostream&out, int indent = 0) const;
+    void visit(ExprVisitor& func);
 
     const Expression*peek_expr() const { return expr_; }
     const Expression*peek_delay() const { return delay_; }