diff --git a/Operation.cpp b/Operation.cpp
index 16a1a7a..8289425 100644
--- a/Operation.cpp
+++ b/Operation.cpp
@@ -5671,7 +5671,9 @@ Operation::OneMoveTestCollisionAvoid( const STRVECTOR& vAxName, const DBLVECTOR&
                     // traslo il riferimento per avere il cilindro centrato sull'asse Y in positivo
                      frHsol.Translate( frHsol.VersZ() * ptMin.z) ;
                     // verifica di collisione tra cilindro e solido
-                     if ( pStm == nullptr  ||  CDeCylClosedSurfTm( frHsol, max( vtDiag.x, vtDiag.y) / 2, vtDiag.z, *pStm, dSafeDist)) {
+                     double dCylR = max( {vtDiag.x / 2, vtDiag.y /2, 10 * EPS_SMALL}) ;
+                     double dCylH = max( vtDiag.z, 10 * EPS_SMALL) ;
+                     if ( pStm == nullptr  ||  CDeCylClosedSurfTm( frHsol, dCylR, dCylH, *pStm, dSafeDist)) {
                         bCollide = true ;
                         break ;
                      }