diff --git a/pub/src/plot.cpp b/pub/src/plot.cpp
index 6921ceda6f7eea9b14894d5d8d9df41352ea2c9d..e6f5f9274610ab4da5e2fd94b7a8b9134ee2e604 100644
--- a/pub/src/plot.cpp
+++ b/pub/src/plot.cpp
@@ -344,7 +344,7 @@ void NPlot::Plot( class CPlot *plot, bool add )
                             double yi = ( (xn[i+1]-xn[i])*yn[i-1] +
                                           (xn[i]-xn[i-1])*yn[i+1] ) /
                                 (xn[i+1]-xn[i-1]);
-                            if ( plot->Y.close_enough( yn[i], yi, 0.005 ) ) {
+                            if ( !plot->Y.close_enough( yn[i], yi, 0.005 ) ) {
                                 xc.push_back( (xn[i-1] + xn[i])/2 );
                                 //cout << "DEB disc " << xc.back() << "\n";
                                 insert_next = true;