BTW, seems a similar error happens in other circumstances, too. Thanks, Michael. In GNU Emacs 25.1.50.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.2) of 2015-11-17 Repository revision: 58e6235007e6761fb9734b942ecff94bf4e9ba68 Windowing system distributor 'The X.Org Foundation', version 11.0.11703000 System Description: Debian GNU/Linux testing (stretch) Configured features: XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 Important settings: value of $LC_ALL: de_DE.utf8 value of $LC_COLLATE: C value of $LC_TIME: C value of $LANG: de_DE.utf8 locale-coding-system: utf-8-unix