diff --git a/smocore/include/concept.h b/smocore/include/concept.h
index f97c3f7..cd3052b 100644
--- a/smocore/include/concept.h
+++ b/smocore/include/concept.h
@@ -31,7 +31,8 @@ public:
 	ComparatorExpression(
 		logic::Operator &op, std::shared_ptr<Comparator> &comparator
 	)
-	:	logic::UnaryExpression(op, comparator)
+	:	logic::UnaryExpression(
+			op, std::static_pointer_cast<logic::Operand>(comparator))
 	{}
 };
 
diff --git a/smocore/include/logic.h b/smocore/include/logic.h
index c52ac91..6e08225 100644
--- a/smocore/include/logic.h
+++ b/smocore/include/logic.h
@@ -40,7 +40,7 @@ class UnaryExpression
 :	public ExpressionPart
 {
 public:
-	UnaryExpression(Operator &op, std::shared_ptr<Operand> &operand)
+	UnaryExpression(Operator &op, const std::shared_ptr<Operand> &operand)
 	:	parts(std::make_pair(op, operand))
 	{}
 public: