While using the monokai theme and helm, a hang can be triggered with a setq header-line-format in a specific shape. The below is a repro from an emacs -Q. This does not repro in Emacs 24 or terminal emacs. I am on OS X. The hang does not repro if there is no :box in the face defined below. With emacs -Q eval the following: ;; https://gist.github.com/aaronjensen/db5eb0b7ba3679971fa2 (deftheme monokai "The Monokai colour theme") (defgroup monokai nil "Monokai theme options. The theme has to be reloaded after changing anything in this group." :group 'faces) (defcustom monokai-distinct-fringe-background nil "Make the fringe background different from the normal background color. Also affects 'linum-mode' background." :type 'boolean :group 'monokai) (defcustom monokai-use-variable-pitch t "Use variable pitch face for some headings and titles." :type 'boolean :group 'monokai) (defcustom monokai-high-contrast-mode-line nil "Make the active/inactive mode line stand out more." :type 'boolean :group 'monokai) (let* ((class '((class color) (min-colors 257))) ;; Primary colors (yellow "#E6DB74") (orange "#FD971F") (red "#F92672") (magenta "#FD5FF0") (violet "#AE81FF") (blue "#66D9EF") (cyan "#A1EFE4") (green "#A6E22E") (gray "#474747") ;; Darker and lighter accented colors (yellow-d "#968B26") (yellow-l "#F3EA98") (orange-d "#A45E0A") (orange-l "#FEB257") (red-d "#A20C41") (red-l "#FC5C94") (magenta-d "#A41F99") (magenta-l "#FE87F4") (violet-d "#562AA6") (violet-l "#C2A1FF") (blue-d "#21889B") (blue-l "#8DE6F7") (cyan-d "#349B8D") (cyan-l "#BBF7EF") (green-d "#67930F") (green-l "#C1F161") (gray-d "#333333") (gray-l "#6b6b6b") ;; Adaptive colors (monokai-fg "#F8F8F2") (monokai-bg "#272822") (monokai-hl "#3E3D31") (monokai-hl-line "#49483E") (monokai-emph "#F8F8F0") (monokai-comments "#75715E") ;; Adaptive higher/lower contrast accented colors (monokai-fg-hc "#141414") (monokai-fg-lc "#171A0B") ;; High contrast colors (yellow-hc yellow-l) (yellow-lc yellow-d) (orange-hc orange-l) (orange-lc orange-d) (red-hc red-l) (red-lc red-d) (magenta-hc magenta-l) (magenta-lc magenta-d) (violet-hc violet-l) (violet-lc violet-d) (blue-hc blue-l) (blue-lc blue-d) (cyan-hc cyan-l) (cyan-lc cyan-d) (green-hc green-l) (green-lc green-d) ;; customize based face properties (s-variable-pitch (if monokai-use-variable-pitch 'variable-pitch 'default)) (s-fringe-bg (if monokai-distinct-fringe-background monokai-hl monokai-bg)) (s-mode-line-fg (if monokai-high-contrast-mode-line monokai-bg monokai-fg)) (s-mode-line-bg (if monokai-high-contrast-mode-line monokai-fg monokai-hl)) (s-mode-line-buffer-id-fg (if monokai-high-contrast-mode-line 'unspecified green)) (s-mode-line-inactive-fg (if monokai-high-contrast-mode-line monokai-fg monokai-comments)) (s-mode-line-inactive-bg (if monokai-high-contrast-mode-line gray-l monokai-bg)) (s-mode-line-inactive-bc (if monokai-high-contrast-mode-line monokai-fg monokai-hl)) ;; powerline (s-powerline-active1-bg (if monokai-high-contrast-mode-line gray-l gray)) (s-powerline-active2-bg (if monokai-high-contrast-mode-line gray gray-l)) (s-powerline-inactive1-bg (if monokai-high-contrast-mode-line gray gray-d)) (s-powerline-inactive2-bg (if monokai-high-contrast-mode-line monokai-bg gray)) ;; Definitions for terminals that do not support 256 colors (terminal-class '((class color) (min-colors 89))) ;; Primary colors (terminal-yellow "#CDC673") (terminal-orange "#FF8C00") (terminal-red "#FF1493") (terminal-magenta "#D700D7") (terminal-violet "#AF87FF") (terminal-blue "#5FD7FF") (terminal-cyan "#5FFFFF") (terminal-green "#87D700") (terminal-gray "#444444") ;; Darker and lighter accented colors (terminal-yellow-d "#878700") (terminal-yellow-l "#FFFF87") (terminal-orange-d "#AF5F00") (terminal-orange-l "#FFAF5F") (terminal-red-d "#870000") (terminal-red-l "#FF5F87") (terminal-magenta-d "#AF0087") (terminal-magenta-l "#FF87DF") (terminal-violet-d "#5F00AF") (terminal-violet-l "#AF87D7") (terminal-blue-d "#008787") (terminal-blue-l "#87D7FF") (terminal-cyan-d "#5FAFAF") (terminal-cyan-l "#AFFFFF") (terminal-green-d "#5F8700") (terminal-green-l "#AFD700") (terminal-gray-d "#3A3A3A") (terminal-gray-l "#6C6C6C") ;; Adaptive colors (terminal-monokai-fg "#F5F5F5") (terminal-monokai-bg "#1B1E1C") (terminal-monokai-hl-line "#212121") (terminal-monokai-hl "#303030") (terminal-monokai-emph "#FFFAFA") (terminal-monokai-comments "#8B8878") ;; Adaptive higher/lower contrast accented colors (terminal-monokai-fg-hc "#171A0B") (terminal-monokai-fg-lc "#141414") ;; High contrast colors (terminal-yellow-hc terminal-yellow-d) (terminal-yellow-lc terminal-yellow-l) (terminal-orange-hc terminal-orange-d) (terminal-orange-lc terminal-orange-l) (terminal-red-hc terminal-red-d) (terminal-red-lc terminal-red-l) (terminal-magenta-hc terminal-magenta-d) (terminal-magenta-lc terminal-magenta-l) (terminal-violet-hc terminal-violet-d) (terminal-violet-lc terminal-violet-l) (terminal-blue-hc terminal-blue-d) (terminal-blue-lc terminal-blue-l) (terminal-cyan-hc terminal-cyan-d) (terminal-cyan-lc terminal-cyan-l) (terminal-green-hc terminal-green-d) (terminal-green-lc terminal-green-l) ;; customize based face properties (terminal-s-variable-pitch (if monokai-use-variable-pitch 'variable-pitch 'default)) (terminal-s-fringe-bg (if monokai-distinct-fringe-background terminal-monokai-hl terminal-monokai-bg)) (terminal-s-mode-line-fg (if monokai-high-contrast-mode-line terminal-monokai-bg terminal-monokai-fg)) (terminal-s-mode-line-bg (if monokai-high-contrast-mode-line terminal-monokai-fg terminal-monokai-hl)) (terminal-s-mode-line-buffer-id-fg (if monokai-high-contrast-mode-line 'unspecified terminal-green)) (terminal-s-mode-line-inactive-fg (if monokai-high-contrast-mode-line terminal-monokai-fg terminal-monokai-comments)) (terminal-s-mode-line-inactive-bg (if monokai-high-contrast-mode-line terminal-monokai-hl-line terminal-monokai-bg)) (terminal-s-mode-line-inactive-bc (if monokai-high-contrast-mode-line terminal-monokai-fg terminal-monokai-hl))) ;; Define faces (custom-theme-set-faces 'monokai `(header-line ((,class (:inverse-video unspecified :underline unspecified :foreground ,monokai-emph :background ,monokai-hl :box (:line-width 1 :color ,monokai-hl :style unspecified))) )) ) ) ;;;###autoload (when (and (boundp 'custom-theme-load-path) load-file-name) (add-to-list 'custom-theme-load-path (file-name-as-directory (file-name-directory load-file-name)))) (provide-theme 'monokai) ;;; monokai-theme.el ends here (defface helm-header-line-left-margin '((t (:foreground "black" :background "yellow"))) "Face used to highlight helm-header sign in left-margin." :group 'helm-faces) (setq header-line-format #(" " 0 1 (display #("->" 0 2 (face helm-header-line-left-margin))))) In GNU Emacs 25.0.92.1 (x86_64-apple-darwin15.3.0, NS appkit-1404.34 Version 10.11.3 (Build 15D21)) of 2016-03-19 built on aaronmbp.local Windowing system distributor 'Apple', version 10.3.1404 Configured using: 'configure --prefix=/usr/local/Cellar/emacs/25.0.92 --enable-locallisppath=/usr/local/share/emacs/site-lisp --infodir=/usr/local/Cellar/emacs/25.0.92/share/info/emacs --with-xml2 --without-dbus --with-gnutls --with-rsvg --with-imagemagick --with-ns --disable-ns-self-contained' Configured features: JPEG RSVG IMAGEMAGICK NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS Important settings: value of $LC_CTYPE: en_US.UTF-8 value of $LANG: en_US.UTF-8 locale-coding-system: utf-8-unix Major mode: Emacs-Lisp 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: Checking 57 files in /usr/local/Cellar/emacs/25.0.92/share/emacs/25.0.92/lisp/eshell... Checking 70 files in /usr/local/Cellar/emacs/25.0.92/share/emacs/25.0.92/lisp/erc... Checking 34 files in /usr/local/Cellar/emacs/25.0.92/share/emacs/25.0.92/lisp/emulation... Checking 168 files in /usr/local/Cellar/emacs/25.0.92/share/emacs/25.0.92/lisp/emacs-lisp... Checking 24 files in /usr/local/Cellar/emacs/25.0.92/share/emacs/25.0.92/lisp/cedet... Checking 57 files in /usr/local/Cellar/emacs/25.0.92/share/emacs/25.0.92/lisp/calendar... Checking 87 files in /usr/local/Cellar/emacs/25.0.92/share/emacs/25.0.92/lisp/calc... Checking 122 files in /usr/local/Cellar/emacs/25.0.92/share/emacs/25.0.92/lisp/obsolete... Checking for load-path shadows...done Making completion list... Load-path shadows: None found. Features: (pp shadow sort mail-extr emacsbug message dired format-spec rfc822 mml mml-sec 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 help-mode easymenu cl-loaddefs pcase cl-lib mail-prsvr mail-utils time-date mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type mwheel ns-win ucs-normalize term/common-win 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 kqueue cocoa ns multi-tty make-network-process emacs) Memory information: ((conses 16 197323 13014) (symbols 48 19546 0) (miscs 40 49 268) (strings 32 15127 5240) (string-bytes 1 436426) (vectors 16 33460) (vector-slots 8 644859 11240) (floats 8 160 241) (intervals 56 325 145) (buffers 976 14)) -- Aaron