I was using vim-tmux-navigator and <C-j> had always worked.

One day, I found it doesn't work anymore.

When doing <C-v><C-j>, <C-v><C-m>, <C-v><enter> in command mode, they all give me ^M. However testing on my colleague's Mac, the <C-j> would return ^@ instead.

All I know is:

  1. The plugin maps <NL> and <CR> instead of some specific keystrokes
  2. :verbose map shows nothing suspicious. No <C-j> mappings. Only mapping <NL> and <CR> to :TmuxNavigateDown.

Any ideas? (I am using iTerm2)

  • 1
    ^@ is the NULL byte (0x00), which is a weird key code to send Commented Dec 21, 2017 at 11:14
  • Last time I have a weird bug is that all my backslashes needs to be double escaped, and the cause was cpoptions. This time I should be using the default cpoptions.. along with Tmux Navigator not working, my :Tags is using path relative to home instead of the project path (so I can't navigate to a tag..) and every time I edit vimrc it says that I have a swap file... Lemme see if I can make a minimal reproducible case for the <C-j> thing
    – Sunny Pun
    Commented Dec 21, 2017 at 16:30
  • @Carpetsmoker I tried vim -u NONE and :nn <NL> ij<esc> and pressing <C-j> doesn't work, but :nn <C-m> ij<esc> would insert the j when I press <C-j>. How may I carry on any investigation?
    – Sunny Pun
    Commented Dec 22, 2017 at 2:27

1 Answer 1


This is indeed a very weird issue. After "fixing", my <C-j> is now returning ^@ and the mapping to <NL> worked.

It should be a Tmux session problem. After turning off tmux and re-attaching the session again, everything is fine.

P.S. for whoever also getting the other issues addressed in the comments, those are really separate issues -- the tags is that I moved tags from project root to .git thus the paths are all wrong; and the vimrc is because there is really a swap file there which is being edited in some halted vim process.

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