diff --git a/src/Model/Geometry/ProfileXYZ.py b/src/Model/Geometry/ProfileXYZ.py
index 2763924b..81fa89dc 100644
--- a/src/Model/Geometry/ProfileXYZ.py
+++ b/src/Model/Geometry/ProfileXYZ.py
@@ -463,11 +463,11 @@ class ProfileXYZ(Profile, SQLSubModel):
         # interpolation des points ptX et ptY
         if (irg > 0):
             x=np.interp(z,
-                        [self.point(irg).z,self.point(irg+1).z],
-                        [self.point(irg).x,self.point(irg+1).x])
+                        [self.point(irg-1).z,self.point(irg).z],
+                        [self.point(irg-1).x,self.point(irg).x])
             y=np.interp(z,
-                        [self.point(irg).z,self.point(irg+1).z],
-                        [self.point(irg).y,self.point(irg+1).y])
+                        [self.point(irg-1).z,self.point(irg).z],
+                        [self.point(irg-1).y,self.point(irg).y])
             ptX=PointXYZ(x,y,z)
         else:
             ptX = self.point(0)