--- a/trunk/src/wings_draw.erl
+++ b/trunk/src/wings_draw.erl
@@ -8,7 +8,7 @@
 %%  See the file "license.terms" for information on usage and redistribution
 %%  of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 %%
-%%     $Id: wings_draw.erl 579 2009-04-18 08:57:43Z bjorng $
+%%     $Id: wings_draw.erl 599 2009-04-24 04:39:31Z bjorng $
 %%
 
 -module(wings_draw).
@@ -122,10 +122,9 @@
     D;
 invalidate_by_mat(#dlo{src_we=We}=D, Changed) ->
     Used = wings_facemat:used_materials(We),
-    case ordsets:intersection(Used, Changed) of
-	[] -> D;
-	[_|_] ->
-	    D#dlo{work=none,edges=none,vs=none,smooth=none,proxy_faces=none}
+    case ordsets:is_disjoint(Used, Changed) of
+	true -> D;
+	false -> D#dlo{work=none,edges=none,vs=none,smooth=none,proxy_faces=none}
     end.
 
 invalidate_sel(#dlo{src_we=#we{id=Id},src_sel=SrcSel}=D,