diff --git a/IntersTriaTria.cpp b/IntersTriaTria.cpp
index 1648017..36ff54b 100644
--- a/IntersTriaTria.cpp
+++ b/IntersTriaTria.cpp
@@ -85,7 +85,7 @@ IntersTriaTria( const Triangle3d& trTria1, const Triangle3d& trTria2, Point3d& p
       return ITTT_NO ;
 
   // se i triangoli sono complanari
-   if ( nresPP == IPPT_OVERLAPS)
+   if ( nresPP == IPPT_OVERLAPS  ||  ( nVertPos1 == 0  &&  nVertNeg1 == 0)  ||  ( nVertPos2 == 0  &&  nVertNeg2 == 0))
       return IntersCoplanarTriaTria( trTria1, trTria2, vTria) ;
 
   // limito la linea di intersezione con il primo triangolo