diff --git a/dumux/io/gnuplotinterface.hh b/dumux/io/gnuplotinterface.hh
index 4d52b5eaa0fc7a5fca50362a6aa32f867931f3e5..be0287683c06127bda39ac2552c27a085e6bb2f1 100644
--- a/dumux/io/gnuplotinterface.hh
+++ b/dumux/io/gnuplotinterface.hh
@@ -434,10 +434,10 @@ private:
     CurveTypeVector curveType_;
     Scalar xRangeMin_;
     Scalar xRangeMax_;
-    Scalar xRangeIsSet_;
+    bool xRangeIsSet_;
     Scalar yRangeMin_;
     Scalar yRangeMax_;
-    Scalar yRangeIsSet_;
+    bool yRangeIsSet_;
     std::string xLabel_;
     std::string yLabel_;
     std::string plotOptions_;