diff --git a/src/bitmessagemain.py b/src/bitmessagemain.py
index ca3ef1a4..64bcea50 100755
--- a/src/bitmessagemain.py
+++ b/src/bitmessagemain.py
@@ -47,6 +47,7 @@ import signal #Used to capture a Ctrl-C keypress so that Bitmessage can shutdown
 from SimpleXMLRPCServer import *
 import json
 from subprocess import call #used when the API must execute an outside program
+import singleton
 
 #For each stream to which we connect, several outgoingSynSender threads will exist and will collectively create 8 connections with peers.
 class outgoingSynSender(threading.Thread):
@@ -3762,6 +3763,9 @@ if useVeryEasyProofOfWorkForTesting:
     shared.networkDefaultPayloadLengthExtraBytes = int(shared.networkDefaultPayloadLengthExtraBytes / 7000)
 
 if __name__ == "__main__":
+    # is the application already running?  If yes then exit.
+    thisapp = singleton.singleinstance()
+
     signal.signal(signal.SIGINT, signal_handler)
     #signal.signal(signal.SIGINT, signal.SIG_DFL)
 
diff --git a/src/singleton.py b/src/singleton.py
new file mode 100644
index 00000000..7ecca3b7
--- /dev/null
+++ b/src/singleton.py
@@ -0,0 +1,61 @@
+#! /usr/bin/env python
+
+import sys
+import os
+import errno
+import tempfile
+from multiprocessing import Process
+
+
+class singleinstance:
+    """
+    Implements a single instance application by creating a lock file based on the full path to the script file.
+
+    This is based upon the singleton class from tendo https://github.com/pycontribs/tendo
+    which is under the Python Software Foundation License version 2    
+    """
+    def __init__(self, flavor_id=""):
+        import sys
+        self.initialized = False
+        basename = os.path.splitext(os.path.abspath(sys.argv[0]))[0].replace("/", "-").replace(":", "").replace("\\", "-") + '-%s' % flavor_id + '.lock'
+        self.lockfile = os.path.normpath(tempfile.gettempdir() + '/' + basename)
+
+        if sys.platform == 'win32':
+            try:
+                # file already exists, we try to remove (in case previous execution was interrupted)
+                if os.path.exists(self.lockfile):
+                    os.unlink(self.lockfile)
+                self.fd = os.open(self.lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR)
+            except OSError:
+                type, e, tb = sys.exc_info()
+                if e.errno == 13:
+                    print 'Another instance of this application is already running'
+                    sys.exit(-1)
+                print(e.errno)
+                raise
+        else:  # non Windows
+            import fcntl
+            self.fp = open(self.lockfile, 'w')
+            try:
+                fcntl.lockf(self.fp, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            except IOError:
+                print 'Another instance of this application is already running'
+                sys.exit(-1)
+        self.initialized = True
+
+    def __del__(self):
+        import sys
+        if not self.initialized:
+            return
+        try:
+            if sys.platform == 'win32':
+                if hasattr(self, 'fd'):
+                    os.close(self.fd)
+                    os.unlink(self.lockfile)
+            else:
+                import fcntl
+                fcntl.lockf(self.fp, fcntl.LOCK_UN)
+                if os.path.isfile(self.lockfile):
+                    os.unlink(self.lockfile)
+        except Exception, e:
+            sys.exit(-1)