diff -urN a/lib/portage/output.py b/lib/portage/output.py
--- a/lib/portage/output.py	2019-02-20 09:44:36.000000000 +0900
+++ b/lib/portage/output.py	2019-03-11 12:13:16.957281932 +0900
@@ -235,6 +235,7 @@
 	return len(tmp)
 
 _legal_terms_re = re.compile(r'^(xterm|xterm-color|Eterm|aterm|rxvt|screen|kterm|rxvt-unicode|gnome|interix|tmux|st-256color)')
+_screen_tmux_re = re.compile(r'^(screen|tmux)')
 _disable_xtermTitle = None
 _max_xtermTitle_len = 253
 
@@ -251,7 +252,10 @@
 		if len(mystr) > _max_xtermTitle_len:
 			mystr = mystr[:_max_xtermTitle_len]
 		if not raw:
-			mystr = '\x1b]0;%s\x07' % mystr
+			if _screen_tmux_re.match(os.environ['TERM']) is None:
+				mystr = '\x1b]0;%s\x07' % mystr
+			else:
+				mystr = '\x1bk%s\x1b\\' % mystr
 
 		# avoid potential UnicodeEncodeError
 		mystr = _unicode_encode(mystr,
@@ -294,9 +298,13 @@
 			home = os.environ.get('HOME', '')
 			if home != '' and pwd.startswith(home):
 				pwd = '~' + pwd[len(home):]
-			default_xterm_title = '\x1b]0;%s@%s:%s\x07' % (
+			default_xterm_title = '%s@%s:%s' % (
 				os.environ.get('LOGNAME', ''),
 				os.environ.get('HOSTNAME', '').split('.', 1)[0], pwd)
+			if _screen_tmux_re.match(os.environ['TERM']) is None:
+				default_xterm_title = '\x1b]0;%s\x07' % default_xterm_title
+			else:
+				default_xterm_title = '\x1bk%s\x1b\\' % default_xterm_title
 	xtermTitle(default_xterm_title, raw=True)
 
 def notitles():