diff --git a/SfrCreate.cpp b/SfrCreate.cpp
index 6cf7a71..96f6671 100644
--- a/SfrCreate.cpp
+++ b/SfrCreate.cpp
@@ -333,7 +333,7 @@ GetSurfFlatRegionFromFatCurve( ICurve* pCrv, double dRadius, bool bSquareEnds, b
    else {   
      // calcolo la fat curve con Voronoi
       ICURVEPOVECTOR vFatCurves ;
-      if ( CalcCurveFatCurve( *pCurve, vFatCurves, dRadius, bSquareEnds, bSquareMids))
+      if ( ! CalcCurveFatCurve( *pCurve, vFatCurves, dRadius, bSquareEnds, bSquareMids))
          return nullptr ;
 
      // costruisco la superficie a partire dalle curve