diff --git a/eoptasks/eoptasks.py b/eoptasks/eoptasks.py
index cd56025..6124f97 100755
--- a/eoptasks/eoptasks.py
+++ b/eoptasks/eoptasks.py
@@ -268,6 +268,10 @@ if not args.cmd:
     sys.exit(1)
 
 def init_tmux_session():
+    if os.environ.get('TMUX'):  # already in a tmux
+        sys.stderr.write('Cannot run embedded in tmux\n')
+        sys.exit(1)
+
     tmux_session_name = 's%s' % random.randrange(1000)
     server_address = '/tmp/.eoptasks.%s' % tmux_session_name
     try: