diff --git a/README.md b/README.md
index 7bc13b7..05bb6ab 100644
--- a/README.md
+++ b/README.md
@@ -52,7 +52,7 @@ for example:
 
 {
   environment.packages = [ pkgs.vim ];
-  system.stateVersion = "20.09";
+  system.stateVersion = "21.05";
 }
 ```
 
@@ -66,7 +66,7 @@ An alternative location is `~/.config/nixpkgs/config.nix` with the key
 
     {
       environment.packages = [ pkgs.vim ];
-      system.stateVersion = "20.09";
+      system.stateVersion = "21.05";
     };
 }
 ```
@@ -80,7 +80,7 @@ To enable `home-manager` you simply need to follow the instructions already prov
 
 1.  Add `home-manager` channel:
     ```
-    nix-channel --add https://github.com/rycee/home-manager/archive/release-20.09.tar.gz home-manager
+    nix-channel --add https://github.com/rycee/home-manager/archive/release-21.05.tar.gz home-manager
     nix-channel --update
     ```
 2.  Configure `home-manager`:
@@ -89,7 +89,7 @@ To enable `home-manager` you simply need to follow the instructions already prov
 
     {
       # Read nix-on-droid changelog before changing this value
-      system.stateVersion = "20.09";
+      system.stateVersion = "21.05";
 
       # insert nix-on-droid config
 
@@ -97,7 +97,7 @@ To enable `home-manager` you simply need to follow the instructions already prov
         { pkgs, ... }:
         {
           # Read home-manager changelog before changing this value
-          home.stateVersion = "20.09";
+          home.stateVersion = "21.05";
 
           # insert home-manager config
         };
@@ -171,7 +171,7 @@ writing a `flake.nix`:
   description = "nix-on-droid configuration";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/release-20.09";
+    nixpkgs.url = "github:NixOS/nixpkgs/release-21.05";
     nix-on-droid.url = "github:t184256/nix-on-droid/master";
     nix-on-droid.inputs.nixpkgs.follows = "nixpkgs";
   };
diff --git a/modules/build/initial-build.nix b/modules/build/initial-build.nix
index 8bc9b71..6547f83 100644
--- a/modules/build/initial-build.nix
+++ b/modules/build/initial-build.nix
@@ -1,4 +1,4 @@
-# Copyright (c) 2019-2020, see AUTHORS. Licensed under MIT License, see LICENSE.
+# Copyright (c) 2019-2021, see AUTHORS. Licensed under MIT License, see LICENSE.
 
 { config, lib, pkgs, ... }:
 
@@ -13,13 +13,13 @@ with lib;
     build.channel = {
       nixpkgs = mkOption {
         type = types.str;
-        default = "https://nixos.org/channels/nixos-20.09";
+        default = "https://nixos.org/channels/nixos-21.05";
         description = "Channel URL for nixpkgs.";
       };
 
       nix-on-droid = mkOption {
         type = types.str;
-        default = "https://github.com/t184256/nix-on-droid/archive/release-20.09.tar.gz";
+        default = "https://github.com/t184256/nix-on-droid/archive/release-21.05.tar.gz";
         description = "Channel URL for nix-on-droid.";
       };
     };
diff --git a/modules/environment/login/nix-on-droid.nix.default b/modules/environment/login/nix-on-droid.nix.default
index cfc903f..66c27ae 100644
--- a/modules/environment/login/nix-on-droid.nix.default
+++ b/modules/environment/login/nix-on-droid.nix.default
@@ -28,17 +28,17 @@
   environment.etcBackupExtension = ".bak";
 
   # Read the changelog before changing this value
-  system.stateVersion = "20.09";
+  system.stateVersion = "21.05";
 
   # After installing home-manager channel like
-  #   nix-channel --add https://github.com/rycee/home-manager/archive/release-20.09.tar.gz home-manager
+  #   nix-channel --add https://github.com/rycee/home-manager/archive/release-21.05.tar.gz home-manager
   #   nix-channel --update
   # you can configure home-manager in here like
   #home-manager.config =
   #  { pkgs, ... }:
   #  {
   #    # Read the changelog before changing this value
-  #    home.stateVersion = "20.09";
+  #    home.stateVersion = "21.05";
   #
   #    # Use the same overlays as the system packages
   #    nixpkgs.overlays = config.nixpkgs.overlays;
diff --git a/modules/home-manager.nix b/modules/home-manager.nix
index 04d5a9b..5d0a35a 100644
--- a/modules/home-manager.nix
+++ b/modules/home-manager.nix
@@ -1,4 +1,4 @@
-# Copyright (c) 2019-2020, see AUTHORS. Licensed under MIT License, see LICENSE.
+# Copyright (c) 2019-2021, see AUTHORS. Licensed under MIT License, see LICENSE.
 
 { config, lib, pkgs, home-manager, ... }:
 
diff --git a/modules/version.nix b/modules/version.nix
index 922de0e..121cf06 100644
--- a/modules/version.nix
+++ b/modules/version.nix
@@ -1,4 +1,4 @@
-# Copyright (c) 2019-2020, see AUTHORS. Licensed under MIT License, see LICENSE.
+# Copyright (c) 2019-2021, see AUTHORS. Licensed under MIT License, see LICENSE.
 
 { config, lib, pkgs, ... }:
 
@@ -11,7 +11,7 @@ with lib;
   options = {
 
     system.stateVersion = mkOption {
-      type = types.enum [ "19.09" "20.03" "20.09" ];
+      type = types.enum [ "19.09" "20.03" "20.09" "21.05" ];
       default = "19.09";
       description = ''
         It is occasionally necessary for nix-on-droid to change