diff --git a/lib/modules.nix b/lib/modules.nix
index 654c4c588de67..f7d522cad397f 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -310,6 +310,7 @@ rec {
 
     in opt //
       { value = addErrorContext "while evaluating the option `${showOption loc}':" value;
+        inherit (res.defsFinal') highestPrio;
         definitions = map (def: def.value) res.defsFinal;
         files = map (def: def.file) res.defsFinal;
         inherit (res) isDefined;
@@ -317,7 +318,7 @@ rec {
 
   # Merge definitions of a value of a given type.
   mergeDefinitions = loc: type: defs: rec {
-    defsFinal =
+    defsFinal' =
       let
         # Process mkMerge and mkIf properties.
         defs' = concatMap (m:
@@ -325,15 +326,20 @@ rec {
         ) defs;
 
         # Process mkOverride properties.
-        defs'' = filterOverrides defs';
+        defs'' = filterOverrides' defs';
 
         # Sort mkOrder properties.
         defs''' =
           # Avoid sorting if we don't have to.
-          if any (def: def.value._type or "" == "order") defs''
-          then sortProperties defs''
-          else defs'';
-      in defs''';
+          if any (def: def.value._type or "" == "order") defs''.values
+          then sortProperties defs''.values
+          else defs''.values;
+      in {
+        values = defs''';
+        inherit (defs'') highestPrio;
+      };
+
+    defsFinal = defsFinal'.values;
 
     # Type-check the remaining definitions, and merge them.
     mergedValue = foldl' (res: def:
@@ -416,13 +422,18 @@ rec {
 
      Note that "z" has the default priority 100.
   */
-  filterOverrides = defs:
+  filterOverrides = defs: (filterOverrides' defs).values;
+
+  filterOverrides' = defs:
     let
       defaultPrio = 100;
       getPrio = def: if def.value._type or "" == "override" then def.value.priority else defaultPrio;
       highestPrio = foldl' (prio: def: min (getPrio def) prio) 9999 defs;
       strip = def: if def.value._type or "" == "override" then def // { value = def.value.content; } else def;
-    in concatMap (def: if getPrio def == highestPrio then [(strip def)] else []) defs;
+    in {
+      values = concatMap (def: if getPrio def == highestPrio then [(strip def)] else []) defs;
+      inherit highestPrio;
+    };
 
   /* Sort a list of properties.  The sort priority of a property is
      1000 by default, but can be overridden by wrapping the property
diff --git a/nixos/doc/manual/release-notes/rl-1803.xml b/nixos/doc/manual/release-notes/rl-1803.xml
index ce58c4dc95b08..469c6a9f338c1 100644
--- a/nixos/doc/manual/release-notes/rl-1803.xml
+++ b/nixos/doc/manual/release-notes/rl-1803.xml
@@ -209,6 +209,9 @@ following incompatible changes:</para>
       For <literal>stateVersion = "17.09"</literal> or lower the old behavior is preserved.
     </para>
     <itemizedlist>
+      <listitem>
+         <literal>sound.enable</literal> now defaults to false.
+      </listitem>
       <listitem>
         <para>
           <literal>matrix-synapse</literal> uses postgresql by default instead of sqlite.
diff --git a/nixos/modules/installer/tools/nixos-generate-config.pl b/nixos/modules/installer/tools/nixos-generate-config.pl
index a82ee63fd0cda..14be5c3e72ce1 100644
--- a/nixos/modules/installer/tools/nixos-generate-config.pl
+++ b/nixos/modules/installer/tools/nixos-generate-config.pl
@@ -603,6 +603,9 @@ sub multiLineList {
   # Enable CUPS to print documents.
   # services.printing.enable = true;
 
+  # Enable sound.
+  # sound.enable = true;
+
   # Enable the X11 windowing system.
   # services.xserver.enable = true;
   # services.xserver.layout = "us";
diff --git a/nixos/modules/misc/version.nix b/nixos/modules/misc/version.nix
index 6af584250a703..275e17f0ce0c8 100644
--- a/nixos/modules/misc/version.nix
+++ b/nixos/modules/misc/version.nix
@@ -1,4 +1,4 @@
-{ config, lib, pkgs, ... }:
+{ options, config, lib, pkgs, ... }:
 
 with lib;
 
@@ -78,6 +78,11 @@ in
 
   config = {
 
+    warnings = lib.optional (options.system.stateVersion.highestPrio == 1001) ''
+      You don't have `system.stateVersion` explicitly set. Expect things to break.
+      See release notes and grep for "stateVersion" in `nixpkgs/nixos` tree.
+    '';
+
     system.nixos = {
       # These defaults are set here rather than up there so that
       # changing them would not rebuild the manual
diff --git a/nixos/modules/services/audio/alsa.nix b/nixos/modules/services/audio/alsa.nix
index acf48d3c3d032..3707bd99039b9 100644
--- a/nixos/modules/services/audio/alsa.nix
+++ b/nixos/modules/services/audio/alsa.nix
@@ -21,7 +21,8 @@ in
 
       enable = mkOption {
         type = types.bool;
-        default = true;
+        default = !versionAtLeast config.system.stateVersion "18.03";
+        defaultText = "!versionAtLeast system.stateVersion \"18.03\"";
         description = ''
           Whether to enable ALSA sound.
         '';