Obtained from: https://bugs.gentoo.org/641514#c2
--- qtiplot/src/scripting/qti.sip.orig	2018-01-02 11:37:07 UTC
+++ qtiplot/src/scripting/qti.sip
@@ -3243,11 +3243,11 @@ class FFT : Filter (public)
 %MethodCode
   SIPQTI_APP(new sipFFT(app, a0, *a1, a2, a3))
 %End
-  FFT(QwtPlotCurve *&) /NoDerived/;
+  FFT(QwtPlotCurve *) /NoDerived/;
 %MethodCode
   SIPQTI_APP(new sipFFT(app, a0))
 %End
-  FFT(QwtPlotCurve *&, double, double) /NoDerived/;
+  FFT(QwtPlotCurve *, double, double) /NoDerived/;
 %MethodCode
   SIPQTI_APP(new sipFFT(app, a0, a1, a2))
 %End