diff --git a/demos/piece-extr.geo b/demos/piece-extr.geo
index 070e28da60f043c0863f0fbf1916912e9652bd5e..906e1823a78a82dbb84b042b1c5a3cff0a509127 100644
--- a/demos/piece-extr.geo
+++ b/demos/piece-extr.geo
@@ -94,3 +94,9 @@ Extrude Surface {91, {0,0,0.2}}{ Layers{ ones[{0:4}],ones[{0:4}], ep2[] }; };
 Extrude Surface {47, {0,0,-0.2}}{ Layers{ ones[{0:4}],ones[{0:4}], ep2[] }; }; 
 
 Physical Volume(1) = 1 ;
+
+Physical Surface(2) = {288,49,215,211,207,203,199,195,191,187,183,179,175,171,
+		       167,163,159,155,151,147,143,139,135,271,267,263,259,255,
+		       251,247,243,239,235,231,227,223,219,372,343,62,301,330,
+		       313,74,355,367,86,325,321,82,363,359,78,317,91,47,347,
+		       66,371,90,305,329,309,70,351};