diff --git a/src/morevna.py b/src/morevna.py
--- a/src/morevna.py
+++ b/src/morevna.py
@@ -7,27 +7,29 @@ from client import Client
 from server import Server
 
 
-def _checkDatafile(datafile):
-	if not os.path.isfile(datafile):
-		print("invalid file specified:",args.datafile,file=sys.stderr)
+def _checkFile(f):
+	if not os.path.isfile(f):
+		print("invalid file specified:",f,file=sys.stderr)
 		sys.exit(1)
 
 
 def buildTree(args):
-	_checkDatafile(args.datafile)
+	_checkFile(args.datafile)
 
 	tree=HashTree.fromFile(args.datafile)
 	tree.save(args.treefile)
 
 def update(args):
-	_checkDatafile(args.datafile)
+	_checkFile(args.datafile)
 
 	c=Client(args.datafile)
 	blocksToTransfer=c.negotiate()
 	c.sendData(blocksToTransfer)
 
 def serve(args):
-	_checkDatafile(args.datafile)
+	_checkFile(args.datafile)
+	if args.tree:
+		_checkFile(args.tree)
 
 	# debug copy default file
 	import shutil
@@ -35,7 +37,7 @@ def serve(args):
 	filename=origFilename+"_"
 	shutil.copyfile(origFilename,filename)
 
-	s=Server(filename)
+	s=Server(filename,args.tree)
 	s.serve()