diff --git a/tutorial/t5.geo b/tutorial/t5.geo
index 1dbce3bec9a175c16accc57bda01aee136225fb3..1a116dd11d1a163f890b3c8a9ea43212930a9d3e 100644
--- a/tutorial/t5.geo
+++ b/tutorial/t5.geo
@@ -103,6 +103,11 @@ Function CheeseHole
   l7 = newreg; Line Loop(l7) = {c2,c7,c12};   Ruled Surface(newreg) = {l7};
   l8 = newreg; Line Loop(l8) = {-c6,-c9,c2};  Ruled Surface(newreg) = {l8};
 
+// Warning: surface meshes are generated by projecting a 2D mesh in
+// the mean plane of the surface. This gives nice results only if the
+// surface curvature is small enough. Otherwise you will have to cut
+// the surface in pieces.
+
 // Arrays of variables can be manipulated in the same way as classical
 // variables. Warning: accessing an uninitialized element in an array
 // will produce an unpredictable result. Note that whole arrays can