diff --git a/config/config.exs b/config/config.exs
index 78a3759..3d474da 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -1,6 +1,6 @@
 # This file is responsible for configuring your application
-# and its dependencies with the aid of the Mix.Config module.
-use Mix.Config
+# and its dependencies with the aid of the Config module.
+import Config
 
 # This configuration is loaded before any dependency and is restricted
 # to this project. If another project depends on this project, this
@@ -21,4 +21,4 @@ use Mix.Config
 #     config :logger, level: :info
 #
 
-import_config "#{Mix.env()}.exs"
+import_config "#{config_env()}.exs"
\ No newline at end of file
diff --git a/config/dev.exs b/config/dev.exs
index d2d855e..becde76 100644
--- a/config/dev.exs
+++ b/config/dev.exs
@@ -1 +1 @@
-use Mix.Config
+import Config
diff --git a/config/prod.exs b/config/prod.exs
index d2d855e..becde76 100644
--- a/config/prod.exs
+++ b/config/prod.exs
@@ -1 +1 @@
-use Mix.Config
+import Config
diff --git a/config/test.exs b/config/test.exs
index b386632..1509595 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -1,4 +1,4 @@
-use Mix.Config
+import Config
 
 config :holidefs,
   locales: [
diff --git a/lib/holidefs.ex b/lib/holidefs.ex
index f2a242c..0f5b35d 100644
--- a/lib/holidefs.ex
+++ b/lib/holidefs.ex
@@ -56,7 +56,7 @@ defmodule Holidefs do
     fed: "Federal Reserve"
   }
 
-  @locale_keys Application.get_env(:holidefs, :locales, Map.keys(@all_locales))
+  @locale_keys Application.compile_env(:holidefs, :locales, Map.keys(@all_locales))
   @locales Map.take(@all_locales, @locale_keys)
 
   @doc """
diff --git a/mix.exs b/mix.exs
index 71dcca4..875a86c 100644
--- a/mix.exs
+++ b/mix.exs
@@ -2,13 +2,13 @@ defmodule Holidefs.Mixfile do
   use Mix.Project
 
   @github_url "https://github.com/toggl/holidefs"
-  @version "0.3.8"
+  @version "0.4.0"
 
   def project do
     [
       app: :holidefs,
       version: @version,
-      elixir: "~> 1.5",
+      elixir: "~> 1.11",
       elixirc_paths: elixirc_paths(Mix.env()),
       package: package(),
       start_permanent: Mix.env() == :prod,