diff --git a/nixos/doc/manual/release-notes/rl-1803.xml b/nixos/doc/manual/release-notes/rl-1803.xml
index 60c17c60413..67e04220681 100644
--- a/nixos/doc/manual/release-notes/rl-1803.xml
+++ b/nixos/doc/manual/release-notes/rl-1803.xml
@@ -418,15 +418,6 @@ following incompatible changes:</para>
       have been added to set up static routing.
     </para>
   </listitem>
-  <listitem>
-    <para>
-      The option <option>services.xserver.desktopManager.default</option> is now
-      <literal>none</literal> by default. An assertion failure is thrown if WM's
-      and DM's default are <literal>none</literal>.
-      To explicitly run a plain X session without and DM or WM, the newly
-      introduced option <option>services.xserver.plainX</option> must be set to true.
-    </para>
-  </listitem>
   <listitem>
     <para>
       The option <option>services.logstash.listenAddress</option> is now <literal>127.0.0.1</literal> by default.
diff --git a/nixos/modules/services/x11/desktop-managers/default.nix b/nixos/modules/services/x11/desktop-managers/default.nix
index 4622c7b760f..f435e85f6b8 100644
--- a/nixos/modules/services/x11/desktop-managers/default.nix
+++ b/nixos/modules/services/x11/desktop-managers/default.nix
@@ -87,11 +87,11 @@ in
 
       default = mkOption {
         type = types.str;
-        default = "none";
-        example = "plasma5";
+        default = "";
+        example = "none";
         description = "Default desktop manager loaded if none have been chosen.";
         apply = defaultDM:
-          if defaultDM == "none" && cfg.session.list != [] then
+          if defaultDM == "" && cfg.session.list != [] then
             (head cfg.session.list).name
           else if any (w: w.name == defaultDM) cfg.session.list then
             defaultDM
diff --git a/nixos/modules/services/x11/window-managers/default.nix b/nixos/modules/services/x11/window-managers/default.nix
index bc420831ad8..e617e55a7a5 100644
--- a/nixos/modules/services/x11/window-managers/default.nix
+++ b/nixos/modules/services/x11/window-managers/default.nix
@@ -62,9 +62,7 @@ in
         example = "wmii";
         description = "Default window manager loaded if none have been chosen.";
         apply = defaultWM:
-          if defaultWM == "none" && cfg.session != []  then
-            (head cfg.session).name
-          else if any (w: w.name == defaultWM) cfg.session then
+          if any (w: w.name == defaultWM) cfg.session then
             defaultWM
           else
             throw "Default window manager (${defaultWM}) not found.";
diff --git a/nixos/modules/services/x11/xserver.nix b/nixos/modules/services/x11/xserver.nix
index f96d3c5afba..e7918cf9d31 100644
--- a/nixos/modules/services/x11/xserver.nix
+++ b/nixos/modules/services/x11/xserver.nix
@@ -161,15 +161,6 @@ in
         '';
       };
 
-      plainX = mkOption {
-        type = types.bool;
-        default = false;
-        description = ''
-          Whether the X11 session can be plain (without DM/WM) and
-          the Xsession script will be used as fallback or not.
-        '';
-      };
-
       autorun = mkOption {
         type = types.bool;
         default = true;
@@ -561,11 +552,6 @@ in
                 + "${toString (length primaryHeads)} heads set to primary: "
                 + concatMapStringsSep ", " (x: x.output) primaryHeads;
       })
-      { assertion = cfg.desktopManager.default == "none" && cfg.windowManager.default == "none" -> cfg.plainX;
-        message = "Either the desktop manager or the window manager shouldn't be `none`! "
-                + "To explicitly allow this, you can also set `services.xserver.plainX` to `true`. "
-                + "The `default` value looks for enabled WMs/DMs and select the first one.";
-      }
     ];
 
     environment.etc =