diff --git a/vhdlpp/expression.h b/vhdlpp/expression.h
index 50c2e8e2c..595734737 100644
--- a/vhdlpp/expression.h
+++ b/vhdlpp/expression.h
@@ -168,6 +168,7 @@ class ExpUnary : public Expression {
       inline const Expression*peek_operand() const { return operand1_; }
 
       const VType*fit_type(Entity*ent, ScopeBase*scope, const VTypeArray*atype) const;
+      const VType*probe_type(Entity*ent, ScopeBase*scope) const;
       int elaborate_expr(Entity*ent, ScopeBase*scope, const VType*ltype);
       void visit(ExprVisitor& func);
 
diff --git a/vhdlpp/expression_elaborate.cc b/vhdlpp/expression_elaborate.cc
index 79fa6c04c..fbe7f0ec2 100644
--- a/vhdlpp/expression_elaborate.cc
+++ b/vhdlpp/expression_elaborate.cc
@@ -376,6 +376,11 @@ const VType*ExpUnary::fit_type(Entity*ent, ScopeBase*scope, const VTypeArray*aty
       return operand1_->fit_type(ent, scope, atype);
 }
 
+const VType*ExpUnary::probe_type(Entity*ent, ScopeBase*scope) const
+{
+      return operand1_->probe_type(ent, scope);
+}
+
 int ExpUnary::elaborate_expr(Entity*ent, ScopeBase*scope, const VType*ltype)
 {
       ivl_assert(*this, ltype != 0);