diff --git a/files/.tmux.conf b/files/.tmux.conf
index 8e936e5..fcbef2b 100644
--- a/files/.tmux.conf
+++ b/files/.tmux.conf
@@ -1,3 +1,10 @@
+# load TMUX_VERSION
+run-shell "\
+	echo #{version} | sed -e 's|\\.| |g' -e 's|[a-z]*$||' |\
+	while read x y; do\
+		tmux set-environment -g TMUX_VERSION \$((x * 100 + y));\
+	done"
+
 # same prefix as `screen`
 set -g prefix C-a
 unbind C-b