diff --git a/src/library.cr b/src/library.cr
index 58cc86b..ef0fb90 100644
--- a/src/library.cr
+++ b/src/library.cr
@@ -369,7 +369,7 @@ class Library
   property dir : String, title_ids : Array(String), scan_interval : Int32,
     storage : Storage, title_hash : Hash(String, Title)
 
-  def self.default
+  def self.default : self
     unless @@default
       @@default = new
     end
diff --git a/src/logger.cr b/src/logger.cr
index b54d495..8c049ed 100644
--- a/src/logger.cr
+++ b/src/logger.cr
@@ -8,7 +8,7 @@ class Logger
 
   @@severity : Log::Severity = :info
 
-  def self.default
+  def self.default : self
     unless @@default
       @@default = new
     end
diff --git a/src/mangadex/api.cr b/src/mangadex/api.cr
index 18462bd..72ead4d 100644
--- a/src/mangadex/api.cr
+++ b/src/mangadex/api.cr
@@ -133,7 +133,7 @@ module MangaDex
   end
 
   class API
-    def self.default
+    def self.default : self
       unless @@default
         @@default = new
       end
diff --git a/src/mangadex/downloader.cr b/src/mangadex/downloader.cr
index 9424e6f..8e77e45 100644
--- a/src/mangadex/downloader.cr
+++ b/src/mangadex/downloader.cr
@@ -82,7 +82,7 @@ module MangaDex
     property downloader : Downloader?
     @path : String
 
-    def self.default
+    def self.default : self
       unless @@default
         @@default = new
       end
@@ -270,7 +270,7 @@ module MangaDex
     @library_path : String = Config.current.library_path
     @downloading = false
 
-    def self.default
+    def self.default : self
       unless @@default
         @@default = new
       end
diff --git a/src/server.cr b/src/server.cr
index 84f5508..8412d0e 100644
--- a/src/server.cr
+++ b/src/server.cr
@@ -9,7 +9,7 @@ class Context
   property storage : Storage
   property queue : MangaDex::Queue
 
-  def self.default
+  def self.default : self
     unless @@default
       @@default = new
     end
diff --git a/src/storage.cr b/src/storage.cr
index e6057e9..e6c0ad9 100644
--- a/src/storage.cr
+++ b/src/storage.cr
@@ -15,7 +15,7 @@ end
 class Storage
   @path : String
 
-  def self.default
+  def self.default : self
     unless @@default
       @@default = new
     end