diff --git a/.gitignore b/.gitignore
index 1d17dae..93e81c0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 .venv
+*~
diff --git a/tivomirror.py b/tivomirror.py
index cc75ef3..9bb6472 100755
--- a/tivomirror.py
+++ b/tivomirror.py
@@ -13,6 +13,7 @@ import http.cookiejar
 import datetime
 import getopt
 import errno
+import fcntl
 import functools
 import logging
 import logging.handlers
@@ -30,11 +31,13 @@ import urllib.request, urllib.error, urllib.parse
 import xml.dom.minidom
 import yaml
 
+from contextlib import contextmanager
 from io import TextIOWrapper
 
 
 class Config:
 	config = '~/.tivo/config.yaml'
+	lockfile = config + '.lock'
 	cookies = "cookies.txt"
 	gig = 1024.0 * 1024 * 1024
 	headers = requests.utils.default_headers()
@@ -382,6 +385,16 @@ class FdLogger(threading.Thread):
 			self.logger.exception("")
 
 
+@contextmanager
+def exclusive():
+	with open(os.path.expanduser(config.lockfile), 'w') as f:
+		try:
+			fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
+		except BlockingIOError as e:
+			raise TivoException('another tivomirror instance is already running')
+		yield 'locked'
+		fcntl.lockf(f, fcntl.LOCK_UN)
+
 @timeout(43200)
 def download_item(item, mak, target):
 	global config
@@ -523,47 +536,50 @@ def mirror(toc, downloaddb, one=False):
 		logger.error("{}: {:.1f} GB available, at least {:.1f} GB needed, stopping".format\
 			(config.targetdir, avail / config.gig, config.minfree / config.gig))
 		sys.exit(1)
-	
-	items = toc.getItems()
-	logger.info("*** {} shows listed".format(len(items)))
-	for item in items:
-		options = wantitem(item, downloaddb)
-		if isinstance(options, str):
-			logger.debug("*** skipping \"{}\": {}".format(item.name, options))
-		else:
-			download_one(item, downloaddb, options)
-			if one:
-				break
+
+	with exclusive() as lock:
+		items = toc.getItems()
+		logger.info("*** {} shows listed".format(len(items)))
+		for item in items:
+			options = wantitem(item, downloaddb)
+			if isinstance(options, str):
+				logger.debug("*** skipping \"{}\": {}".format(item.name, options))
+			else:
+				download_one(item, downloaddb, options)
+				if one:
+					break
 
 
 def download_episode(toc, downloaddb, episode):
-	items = toc.getItems()
-	options = {}
-	for item in items:
-		if item.title == episode or item.name == episode or item.episode == episode:
-			for i in (item.title, item.episode, item.name):
-				if i in IncludeShow.includes:
-					options = IncludeShow.includes[i]
-					download_one(item, downloaddb, options)
-					return
+	with exclusive() as lock:
+		items = toc.getItems()
+		options = {}
+		for item in items:
+			if item.title == episode or item.name == episode or item.episode == episode:
+				for i in (item.title, item.episode, item.name):
+					if i in IncludeShow.includes:
+						options = IncludeShow.includes[i]
+						download_one(item, downloaddb, options)
+						return
 
 
 def printtoc(toc, downloaddb):
-	items = toc.getItems()
-	print("*** {} shows listed".format(len(items)))
-	shows = {}
-	for item in items:
-		if item.title not in shows:
-			shows[item.title] = []
-		shows[item.title].append(item)
-	for title in sorted(shows):
-		for item in sorted(shows[title], key=lambda i: i.name):
-			options = wantitem(item, downloaddb)
-			if isinstance(options, str):
-				print("{:>7.7s}: {}".format(options, item.name))
-				continue
-			print("*** downloading {} ({:.3f} GB)".format(item.name, item.sourcesize / 1e9))
-	print("*** {} shows listed".format(len(items)))
+	with exclusive() as lock:
+		items = toc.getItems()
+		print("*** {} shows listed".format(len(items)))
+		shows = {}
+		for item in items:
+			if item.title not in shows:
+				shows[item.title] = []
+			shows[item.title].append(item)
+		for title in sorted(shows):
+			for item in sorted(shows[title], key=lambda i: i.name):
+				options = wantitem(item, downloaddb)
+				if isinstance(options, str):
+					print("{:>7.7s}: {}".format(options, item.name))
+					continue
+				print("*** downloading {} ({:.3f} GB)".format(item.name, item.sourcesize / 1e9))
+		print("*** {} shows listed".format(len(items)))
 
 
 def usage():