diff --git a/src/core/mergedproxymodel.h b/src/core/mergedproxymodel.h
index 92b4ee3f1..2d76124ac 100644
--- a/src/core/mergedproxymodel.h
+++ b/src/core/mergedproxymodel.h
@@ -18,6 +18,8 @@
 #ifndef MERGEDPROXYMODEL_H
 #define MERGEDPROXYMODEL_H
 
+#include <functional>
+
 #include <QAbstractProxyModel>
 
 using std::placeholders::_1;