diff --git a/libnatspec/NatspecExpressionEvaluator.h b/libnatspec/NatspecExpressionEvaluator.h
index fc122084e..2ea224027 100644
--- a/libnatspec/NatspecExpressionEvaluator.h
+++ b/libnatspec/NatspecExpressionEvaluator.h
@@ -19,6 +19,8 @@
  * @date 2015
  */
 
+#pragma once
+
 #include <QtCore/QObject>
 #include <QtCore/QtCore>
 #include <QtQml/QJSEngine>