--- a/rc/bashrc	Mon May 16 18:21:24 2016 +0900
+++ b/rc/bashrc	Tue May 31 21:33:55 2016 +0900
@@ -15,6 +15,15 @@
 
 _org_path="${PATH}"
 
+# ensure correct window size at all time
+# noticeably in FreebSD + tmux + vim:
+# 1. start tmux
+# 2. start vim in the session
+# 3. split pane
+# 4. quit vim
+# 5. wrong COLUMNS or LINES
+shopt -s checkwinsize
+
 # Basic PATH
 export PATH="/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:/usr/games"