diff --git a/elixir-format.el b/elixir-format.el
index 3d96924b..6c2ab224 100644
--- a/elixir-format.el
+++ b/elixir-format.el
@@ -28,11 +28,13 @@
 (defcustom elixir-format-arguments nil
   "Additional arguments to 'mix format'"
   :type '(repeat string)
+  :group 'elixir
   :group 'elixir-format)
 
 (defcustom elixir-format-hook nil
   "Hook called by `elixir-format'."
   :type 'hook
+  :group 'elixir
   :group 'elixir-format)
 
 
diff --git a/elixir-mode.el b/elixir-mode.el
index 48e6f24b..10d755b6 100644
--- a/elixir-mode.el
+++ b/elixir-mode.el
@@ -1,4 +1,4 @@
-;;; elixir-mode.el --- Major mode for editing Elixir files
+;;; elixir-mode.el --- Major mode for editing Elixir files -*- lexical-binding: t -*-
 
 ;; Copyright 2011-2015 secondplanet
 ;;           2013-2015 Samuel Tonini, Matt DeBoard, Andreas Fuchs
@@ -10,7 +10,7 @@
 ;; URL: https://github.com/elixir-editors/emacs-elixir
 ;; Created: Mon Nov 7 2011
 ;; Keywords: languages elixir
-;; Version: 2.3.1
+;; Version: 2.4.0
 ;; Package-Requires: ((emacs "24") (pkg-info "0.4"))
 
 ;; This file is not a part of GNU Emacs.
@@ -48,13 +48,17 @@
   :link '(url-link :tag "Github" "https://github.com/elixir-editors/emacs-elixir")
   :link '(emacs-commentary-link :tag "Commentary" "elixir-mode"))
 
-(defvar elixir-mode-website-url "http://elixir-lang.org"
-  "Official url of Elixir programming website.")
+(defcustom elixir-mode-website-url "http://elixir-lang.org"
+  "Official url of Elixir programming website."
+  :type 'string)
 
-(defvar elixir-mode-doc-url "https://hexdocs.pm/elixir"
-  "Official documentation for the Elixir programming language.")
+(defcustom elixir-mode-doc-url "https://hexdocs.pm/elixir"
+  "Official documentation for the Elixir programming language."
+  :type 'string)
 
-(defvar elixir-mode-hook nil)
+(defcustom elixir-mode-hook nil
+  "Hook that runs when switching to major mode"
+  :type 'hook)
 
 (defvar elixir-mode-map
   (let ((map (make-sparse-keymap)))
@@ -72,21 +76,36 @@
     ("Tests" "^\\s-*test[ \t\n]+\"?\\(:?[a-z0-9_@+() \t-]+\\)\"?[ \t\n]+.*" 1))
   "Imenu pattern for `elixir-mode'.")
 
-(defvar elixir-basic-offset 2)
-(defvar elixir-key-label-offset 0)
-(defvar elixir-match-label-offset 2)
+(defcustom elixir-basic-offset 2
+  "Basic offset."
+  :type 'integer)
+(defcustom elixir-key-label-offset 0
+  "Offset used for key label."
+  :type 'integer)
+(defcustom elixir-match-label-offset 2
+  "Offset for a match label."
+  :type 'integer)
+
+(defgroup elixir-faces nil
+  "Font-lock faces for `elixir'."
+  :group 'elixir
+  :group 'faces)
 
 (defvar elixir-attribute-face 'elixir-attribute-face)
 (defface elixir-attribute-face
   '((t (:inherit font-lock-preprocessor-face)))
-  "For use with module attribute tokens."
-  :group 'font-lock-faces)
+  "For use with module attribute tokens.")
 
 (defvar elixir-atom-face 'elixir-atom-face)
 (defface elixir-atom-face
   '((t (:inherit font-lock-builtin-face)))
-  "For use with atoms & map keys."
-  :group 'font-lock-faces)
+  "For use with atoms & map keys.")
+
+(defvar elixir-number-face 'elixir-number-face)
+(defface elixir-number-face
+  '((t (:inherit default)))
+  "For use with numbers.")
+
 
 (eval-when-compile
   (defconst elixir-rx-constituents
@@ -107,6 +126,11 @@
                       (zero-or-more (any "a-z" "A-Z" "0-9" "_" "\"" "'" "!" "@" "?")))
                      (and "\"" (one-or-more (not (any "\""))) "\"")
                      (and "'" (one-or-more (not (any "'"))) "'"))))
+      (numbers . ,(rx (and symbol-start
+                           (? "-")
+                           (+ digit)
+                           (0+ (and "_" (= 3 digit)))
+                           symbol-end)))
       (builtin . ,(rx symbol-start
                       (or "case" "cond" "for" "if" "quote" "raise" "receive" "send"
                           "super" "throw" "try" "unless" "unquote" "unquote_splicing"
@@ -382,6 +406,10 @@ is used to limit the scan."
                  (optional "="))
      1 elixir-atom-face)
 
+    ;; Numbers
+    (,(elixir-rx (group numbers))
+     1 elixir-number-face)
+
     ;; Gray out variables starting with "_"
     (,(elixir-rx symbol-start
                  (group (and "_"