diff --git a/_epub/.formatter.exs b/_epub/.formatter.exs
new file mode 100644
index 000000000..d2cda26ed
--- /dev/null
+++ b/_epub/.formatter.exs
@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]
diff --git a/_epub/lib/elixir_lang_guide.ex b/_epub/lib/elixir_lang_guide.ex
index 2f6ab2e19..3a286e685 100644
--- a/_epub/lib/elixir_lang_guide.ex
+++ b/_epub/lib/elixir_lang_guide.ex
@@ -189,7 +189,10 @@ defmodule ElixirLangGuide do
     stable = elixir_versions[current_stable_version]
 
     content
-    |> String.replace("{% assign stable = site.data.elixir-versions[site.data.elixir-versions.stable] %}", "")
+    |> String.replace(
+      "{% assign stable = site.data.elixir-versions[site.data.elixir-versions.stable] %}",
+      ""
+    )
     |> String.replace("{{ stable.version }}", "#{stable["version"]}")
     |> String.replace("{{ stable.minimum_otp }}", "#{stable["minimum_otp"]}")
   end
diff --git a/_epub/mix.exs b/_epub/mix.exs
index fa3b0f512..05dbe1b9a 100644
--- a/_epub/mix.exs
+++ b/_epub/mix.exs
@@ -2,13 +2,15 @@ defmodule ElixirLangGuide.Mixfile do
   use Mix.Project
 
   def project do
-    [app: :elixir_lang_guide,
-     version: "0.1.0",
-     elixir: "~> 1.4",
-     build_embedded: Mix.env == :prod,
-     start_permanent: Mix.env == :prod,
-     deps: deps(),
-     aliases: [epub: &epub/1]]
+    [
+      app: :elixir_lang_guide,
+      version: "0.1.0",
+      elixir: "~> 1.4",
+      build_embedded: Mix.env() == :prod,
+      start_permanent: Mix.env() == :prod,
+      deps: deps(),
+      aliases: [epub: &epub/1]
+    ]
   end
 
   def application do
@@ -16,13 +18,11 @@ defmodule ElixirLangGuide.Mixfile do
   end
 
   defp epub(_args) do
-    Mix.Task.run "app.start"
+    Mix.Task.run("app.start")
     ElixirLangGuide.run("..")
   end
 
   defp deps do
-    [{:yaml_elixir, "~> 1.3"},
-     {:earmark, "~> 1.0"},
-     {:bupe, "~> 0.3.0"}]
+    [{:yaml_elixir, "~> 1.3"}, {:earmark, "~> 1.0"}, {:bupe, "~> 0.3.0"}]
   end
 end