If I load eieio and byte-compile a function, then some errors are ignored. To reproduce, 1. Start emacs with emacs -Q. 2. Evaluate the following form. (progn (require 'eieio) (defun my-this-should-raise-error () (/ 1 0) (+ 1 2)) (byte-compile 'my-this-should-raise-error) (my-this-should-raise-error)) This should raise the arith-error but it returns 3 without errors. Can someone else reproduce this? Best regards, Sho Takemori In GNU Emacs 25.0.93.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.7) of 2016-05-13 built on HP500-270jp Repository revision: 66cd4d8bd031fb5cb1c65e3b008681021ea32906 Windowing system distributor 'The X.Org Foundation', version 11.0.11702000 System Description: Ubuntu 15.10 Configured features: XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 Important settings: value of $LANG: ja_JP.UTF-8 value of $XMODIFIERS: @im=ibus locale-coding-system: utf-8-unix Major mode: Lisp Interaction Minor modes in effect: tooltip-mode: t global-eldoc-mode: t electric-indent-mode: t mouse-wheel-mode: t tool-bar-mode: t menu-bar-mode: t file-name-shadow-mode: t global-font-lock-mode: t font-lock-mode: t blink-cursor-mode: t auto-composition-mode: t auto-encryption-mode: t auto-compression-mode: t line-number-mode: t transient-mark-mode: t Recent messages: For information about GNU Emacs and the GNU system, type C-h C-a. Mark set 3 (#o3, #x3, ?\C-c) Load-path shadows: None found. Features: (shadow sort mail-extr emacsbug message dired format-spec rfc822 mml mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util help-fns mail-prsvr mail-utils eieio byte-opt bytecomp byte-compile cl-extra help-mode easymenu cconv eieio-core cl-macs gv cl-loaddefs pcase cl-lib time-date mule-util japan-util tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode prog-mode register page menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock syntax facemenu font-core frame cl-generic cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european ethiopic indian cyrillic chinese charscript case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice loaddefs button faces cus-face macroexp files text-properties overlay sha1 md5 base64 format env code-pages mule custom widget hashtable-print-readable backquote dbusbind inotify dynamic-setting system-font-setting font-render-setting move-toolbar gtk x-toolkit x multi-tty make-network-process emacs) Memory information: ((conses 16 98112 5616) (symbols 48 20752 0) (miscs 40 474 82) (strings 32 17493 4672) (string-bytes 1 522963) (vectors 16 14345) (vector-slots 8 533787 4648) (floats 8 193 12) (intervals 56 208 0) (buffers 976 11) (heap 1024 33967 958))