diff --git a/Geo/MVertex.cpp b/Geo/MVertex.cpp
index d0c540e160f49236b86e125f6a16b6a011706241..59fc756234ea619e1d59adee607e34895d0971fa 100644
--- a/Geo/MVertex.cpp
+++ b/Geo/MVertex.cpp
@@ -32,7 +32,7 @@ bool MVertexLessThanNum::operator()(const MVertex *v1, const MVertex *v2) const
   return false;
 }
 
-double angle3Vertices(MVertex *p1, MVertex *p2, MVertex *p3)
+double angle3Vertices(const MVertex *p1, const MVertex *p2, const MVertex *p3)
 {
   SVector3 a(p1->x() - p2->x(), p1->y() - p2->y(), p1->z() - p2->z());
   SVector3 b(p3->x() - p2->x(), p3->y() - p2->y(), p3->z() - p2->z());
diff --git a/Geo/MVertex.h b/Geo/MVertex.h
index 1bcb2ef29314407c72d0816ed633a6b99415081e..1f506d7160da90b2c98e6f3f56aec0ec9b0d9209 100644
--- a/Geo/MVertex.h
+++ b/Geo/MVertex.h
@@ -170,7 +170,7 @@ bool reparamMeshVertexOnFace(MVertex *v, const GFace *gf, SPoint2 &param,
                              bool onSurface=true);
 bool reparamMeshVertexOnEdge(MVertex *v, const GEdge *ge, double &param);
 
-double angle3Vertices(MVertex *p1, MVertex *p2, MVertex *p3);
+double angle3Vertices(const MVertex *p1, const MVertex *p2, const MVertex *p3);
 
 inline double distance (MVertex *v1, MVertex *v2){
   const double dx = v1->x() - v2->x();