diff --git a/.hydra/declarative-jobsets.nix b/.hydra/declarative-jobsets.nix
index 4feaf69..a71242b 100644
--- a/.hydra/declarative-jobsets.nix
+++ b/.hydra/declarative-jobsets.nix
@@ -17,7 +17,7 @@ let
       flake = "gitlab:simple-nixos-mailserver/nixos-mailserver/merge-requests/${info.iid}/head";
     }
   ) prs;
-  # This could be removed once branch 20.09 and 21.05 would have been
+  # This could be removed once branch 21.11 would have been
   # removed.
   mkJobset = branch: {
     description = "Build ${branch} branch of Simple NixOS MailServer";
@@ -61,7 +61,6 @@ let
 
   desc = prJobsets // {
     "master" = mkFlakeJobset "master";
-    "nixos-21.05" = mkJobset "nixos-21.05";
     "nixos-21.11" = mkFlakeJobset "nixos-21.11";
   };
 
diff --git a/README.md b/README.md
index c77cf24..794a12c 100644
--- a/README.md
+++ b/README.md
@@ -83,7 +83,7 @@ D9FE 4119 F082 6F15 93BD  BD36 6162 DBA5 635E A16A
 
 ```nix
    { config, pkgs, ... }:
-   let release = "nixos-21.05";
+   let release = "nixos-21.11";
    in {
      imports = [
        (builtins.fetchTarball {
diff --git a/flake.lock b/flake.lock
index 3580349..d78f8a8 100644
--- a/flake.lock
+++ b/flake.lock
@@ -31,21 +31,6 @@
         "type": "indirect"
       }
     },
-    "nixpkgs-21_05": {
-      "locked": {
-        "lastModified": 1625692408,
-        "narHash": "sha256-e9L3TLLDVIJpMnHtiNHJE62oOh6emRtSZ244bgYJUZs=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "c06613c25df3fe1dd26243847a3c105cf6770627",
-        "type": "github"
-      },
-      "original": {
-        "id": "nixpkgs",
-        "ref": "nixos-21.05",
-        "type": "indirect"
-      }
-    },
     "nixpkgs-21_11": {
       "locked": {
         "lastModified": 1638371214,
@@ -65,7 +50,6 @@
       "inputs": {
         "blobs": "blobs",
         "nixpkgs": "nixpkgs",
-        "nixpkgs-21_05": "nixpkgs-21_05",
         "nixpkgs-21_11": "nixpkgs-21_11",
         "utils": "utils"
       }
diff --git a/flake.nix b/flake.nix
index 33e433e..f7c35c8 100644
--- a/flake.nix
+++ b/flake.nix
@@ -4,7 +4,6 @@
   inputs = {
     utils.url = "github:numtide/flake-utils";
     nixpkgs.url = "flake:nixpkgs/nixos-unstable";
-    nixpkgs-21_05.url = "flake:nixpkgs/nixos-21.05";
     nixpkgs-21_11.url = "flake:nixpkgs/nixos-21.11";
     blobs = {
       url = "gitlab:simple-nixos-mailserver/blobs";
@@ -12,7 +11,7 @@
     };
   };
 
-  outputs = { self, utils, blobs, nixpkgs, nixpkgs-21_05, nixpkgs-21_11 }: let
+  outputs = { self, utils, blobs, nixpkgs, nixpkgs-21_11 }: let
     system = "x86_64-linux";
     pkgs = nixpkgs.legacyPackages.${system};
     # We want to test nixos-mailserver on several nixos releases
@@ -21,10 +20,6 @@
         name = "unstable";
         pkgs = nixpkgs.legacyPackages.${system};
       }
-      {
-        name = "21_05";
-        pkgs = nixpkgs-21_05.legacyPackages.${system};
-      }
       {
         name = "21_11";
         pkgs = nixpkgs-21_11.legacyPackages.${system};
@@ -54,7 +49,7 @@
 
     mailserverModule = import ./.;
 
-    # Generate a rst file describing options of the NixOS mailserver module 
+    # Generate a rst file describing options of the NixOS mailserver module
     generateRstOptions = let
       eval = import (pkgs.path + "/nixos/lib/eval-config.nix") {
         inherit system;
@@ -68,7 +63,7 @@
             mailserver.fqdn = "mx.example.com";
           }
         ];
-        
+
       };
       options = pkgs.nixosOptionsDoc {
         options = eval.options;