diff --git a/.tmux.conf b/.tmux.conf
index 98b0a40..12e2cef 100644
--- a/.tmux.conf
+++ b/.tmux.conf
@@ -29,7 +29,7 @@ bind e new-window -n '~/.tmux.conf' '${EDITOR:-vim} ~/.tmux.conf && tmux source
 bind r source-file ~/.tmux.conf \; display '~/.tmux.conf sourced'
 
 # see https://github.com/ChrisJohnsen/tmux-MacOSX-pasteboard
-set -g default-command '$(command -v reattach-to-user-namespace && echo '-l') $SHELL'
+if 'command -v reattach-to-user-namespace' 'set -g default-command "reattach-to-user-namespace -l $SHELL"'
 
 
 # -- display -------------------------------------------------------------------