https://github.com/KDE/labplot/commit/c2db2ec28aa8958f7041ae5cd03ddae9f44e5aa3
Index: src/backend/worksheet/plots/cartesian/XYFourierFilterCurve.cpp
--- src/backend/worksheet/plots/cartesian/XYFourierFilterCurve.cpp.orig
+++ src/backend/worksheet/plots/cartesian/XYFourierFilterCurve.cpp
@@ -24,6 +24,7 @@ extern "C" {
 #include "backend/nsl/nsl_sf_poly.h"
 }
 
+#include <QElapsedTimer>
 #include <QDebug> // qWarning()
 #include <QIcon>
 #include <QThreadPool>
