diff --git a/Envelope_3/include/CGAL/Env_plane_traits_3.h b/Envelope_3/include/CGAL/Env_plane_traits_3.h
index 3f9fb48b4cb5..d0eb60494621 100644
--- a/Envelope_3/include/CGAL/Env_plane_traits_3.h
+++ b/Envelope_3/include/CGAL/Env_plane_traits_3.h
@@ -239,7 +239,7 @@ class Env_plane_traits_3 : public ArrLinearTraits {
       const Line_2& line = cv.supp_line();
       const FT& a3 = line.a();
       const FT& b3 = line.b();
-      const FT& c3 = line.c();
+      // const FT& c3 = line.c();       // unused
 
       // if the line was parallel to the y-axis (i.e x = const),
       // then it was enough to compare dz/dx of both planes
diff --git a/Envelope_3/include/CGAL/Env_sphere_traits_3.h b/Envelope_3/include/CGAL/Env_sphere_traits_3.h
index 67959b4ebe3b..3d272f81b29f 100644
--- a/Envelope_3/include/CGAL/Env_sphere_traits_3.h
+++ b/Envelope_3/include/CGAL/Env_sphere_traits_3.h
@@ -976,7 +976,7 @@ class Env_sphere_traits_3 : public ConicTraits_2 {
     const Rational& t = cv.t();
     const Rational& u = cv.u();
     const Rational& v = cv.v();
-    const Rational& w = cv.w();
+    // const Rational& w = cv.w();      // unused
     Algebraic m = -1 * (2*r*x0 + t*y0 + u);
     Algebraic n = 2*s*y0 + t*x0 + v;
     // line coefficients: A3, B3, C3