diff -r c481f6bfb19b -r fdcc139587a3 lvm.js
--- a/lvm.js	Sun Nov 21 16:28:17 2010 +0000
+++ b/lvm.js	Sun Nov 21 16:28:40 2010 +0000
@@ -805,7 +805,11 @@
 	if(currframe)
 	{
 		var currfunc = currframe.f;
-		sys.print("lvm.js: "+(currfunc.sourceName||"=<unknown>").substr(1)+":"+(currfunc.sourceLines[currframe.pc]||"<unknown>")+": ");
+		var sourceName = (currfunc.sourceName||"=<unknown>").substr(1);
+		var line = "?";
+		if(currfunc.sourceLines && currfunc.sourceLines[currframe.pc])
+			line = currfunc.sourceLines[currframe.pc];
+		sys.print("lvm.js: "+sourceName+":"+line+": ");
 	}
 	sys.puts(e);
 	if(typeof(e) == "object" && "stack" in e)