diff --git a/gertty/app.py b/gertty/app.py
index 571327a..50c217c 100644
--- a/gertty/app.py
+++ b/gertty/app.py
@@ -16,6 +16,7 @@
 import argparse
 import datetime
 import dateutil
+import fcntl
 import functools
 import logging
 import os
@@ -274,6 +275,13 @@ class App(object):
         self.log = logging.getLogger('gertty.App')
         self.log.debug("Starting")
 
+        self.lock_fd = open(self.config.lock_file, 'w')
+        try:
+            fcntl.lockf(self.lock_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+        except IOError:
+            print("error: another instance of gertty is running for: %s" % self.config.server['name'])
+            sys.exit(1)
+
         self.project_cache = ProjectCache()
         self.ring = mywid.KillRing()
         self.input_buffer = []
diff --git a/gertty/config.py b/gertty/config.py
index dce9a6c..cf38b11 100644
--- a/gertty/config.py
+++ b/gertty/config.py
@@ -186,6 +186,8 @@ class Config(object):
         self.socket_path = os.path.expanduser(socket_path)
         log_file = server.get('log-file', '~/.gertty.log')
         self.log_file = os.path.expanduser(log_file)
+        lock_file = server.get('lock-file', '~/.gertty.%s.lock' % server['name'])
+        self.lock_file = os.path.expanduser(lock_file)
 
         self.palettes = {'default': gertty.palette.Palette({}),
                          'light': gertty.palette.Palette(gertty.palette.LIGHT_PALETTE),