diff --git a/lib/modules.nix b/lib/modules.nix
index a3c3fe7fc1ae..dcede0c46c63 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -17,51 +17,51 @@ rec {
      evalModules) and the less declarative the module set is. */
   evalModules = { modules
                 , prefix ? []
-                , # !!! This can be specified modularly now, can we remove it?
+                , # This would be remove in the future, Prefer _module.args option instead.
                   args ? {}
-                , # !!! This can be specified modularly now, can we remove it?
+                , # This would be remove in the future, Prefer _module.check option instead.
                   check ? true
                 }:
     let
+      # This internal module declare internal options under the `_module'
+      # attribute.  These options are fragile, as they are used by the
+      # module system to change the interpretation of modules.
       internalModule = rec {
         _file = ./modules.nix;
 
         key = _file;
 
         options = {
-          __internal.args = mkOption {
-            description = "Arguments passed to each module.";
-
-            # !!! Should this be types.uniq types.unspecified?
+          _module.args = mkOption {
             type = types.attrsOf types.unspecified;
-
             internal = true;
+            description = "Arguments passed to each module.";
           };
 
-          __internal.check = mkOption {
-            description = "Whether to check whether all option definitions have matching declarations.";
-
+          _module.check = mkOption {
             type = types.uniq types.bool;
-
             internal = true;
-
             default = check;
+            description = "Whether to check whether all option definitions have matching declarations.";
           };
         };
 
         config = {
-          __internal.args = args;
+          _module.args = args;
         };
       };
+
       closed = closeModules (modules ++ [ internalModule ]) { inherit config options; lib = import ./.; };
+
       # Note: the list of modules is reversed to maintain backward
       # compatibility with the old module system.  Not sure if this is
       # the most sensible policy.
       options = mergeModules prefix (reverseList closed);
+
       # Traverse options and extract the option values into the final
       # config set.  At the same time, check whether all option
       # definitions have matching declarations.
-      # !!! __internal.check's value can't depend on any other config values
+      # !!! _module.check's value can't depend on any other config values
       # without an infinite recursion. One way around this is to make the
       # 'config' passed around to the modules be unconditionally unchecked,
       # and only do the check in 'result'.
@@ -71,7 +71,7 @@ rec {
           if isOption v then v.value
           else yieldConfig (prefix ++ [n]) v) set) ["_definedNames"];
         in
-        if options.__internal.check.value && set ? _definedNames then
+        if options._module.check.value && set ? _definedNames then
           fold (m: res:
             fold (name: res:
               if set ? ${name} then res else throw "The option `${showOption (prefix ++ [name])}' defined in `${m.file}' does not exist.")
@@ -122,7 +122,7 @@ rec {
     let
       # Module arguments are resolved in a strict manner when attribute set
       # deconstruction is used.  As the arguments are now defined with the
-      # config.__interanl.args option, the strictness used on the attribute
+      # config._module.args option, the strictness used on the attribute
       # set argument would cause an infinite loop, if the result of the
       # option is given as argument.
       #
@@ -135,7 +135,7 @@ rec {
       requiredArgs = builtins.attrNames (builtins.functionArgs f);
       extraArgs = builtins.listToAttrs (map (name: {
         inherit name;
-        value = config.__internal.args.${name};
+        value = config._module.args.${name};
       }) requiredArgs);
     in f (extraArgs // arg)
   else
diff --git a/lib/types.nix b/lib/types.nix
index f836b07e335f..f22c76616345 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -200,7 +200,6 @@ rec {
             modules = opts' ++ map (def: { _file = def.file; imports = [(coerce def.value)]; }) defs;
           in (evalModules {
             inherit modules;
-            # !!! See comment about args in lib/modules.nix
             args.name = last loc;
             prefix = loc;
           }).config;
diff --git a/nixos/lib/eval-config.nix b/nixos/lib/eval-config.nix
index a157ffd56951..adacbd0863e3 100644
--- a/nixos/lib/eval-config.nix
+++ b/nixos/lib/eval-config.nix
@@ -35,7 +35,7 @@ let
     key = _file;
     config = {
       nixpkgs.system = lib.mkDefault system_;
-      __internal.args.pkgs = lib.mkIf (pkgs_ != null) (lib.mkForce pkgs_);
+      _module.args.pkgs = lib.mkIf (pkgs_ != null) (lib.mkForce pkgs_);
     };
   };
 
@@ -60,5 +60,5 @@ in rec {
     inherit modules baseModules;
   };
 
-  inherit (config.__internal.args) pkgs;
+  inherit (config._module.args) pkgs;
 }
diff --git a/nixos/modules/misc/extra-arguments.nix b/nixos/modules/misc/extra-arguments.nix
index 9943a6192a69..c2c8903546d5 100644
--- a/nixos/modules/misc/extra-arguments.nix
+++ b/nixos/modules/misc/extra-arguments.nix
@@ -1,7 +1,7 @@
 { lib, pkgs, config, ... }:
 
 {
-  __internal.args = {
+  _module.args = {
     modulesPath = ../.;
 
     pkgs_i686 = import ../../lib/nixpkgs.nix {
diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index 2b648c1fa4ed..395ba82f2d16 100644
--- a/nixos/modules/misc/nixpkgs.nix
+++ b/nixos/modules/misc/nixpkgs.nix
@@ -72,7 +72,7 @@ in
   };
 
   config = {
-    __internal.args.pkgs = import ../../lib/nixpkgs.nix {
+    _module.args.pkgs = import ../../lib/nixpkgs.nix {
       system = config.nixpkgs.system;
 
       inherit (config.nixpkgs) config;
diff --git a/nixos/modules/rename.nix b/nixos/modules/rename.nix
index b898dc23522d..087b903b8f49 100644
--- a/nixos/modules/rename.nix
+++ b/nixos/modules/rename.nix
@@ -136,7 +136,7 @@ in zipModules ([]
 
 ++ obsolete [ "services" "mysql55" ] [ "services" "mysql" ]
 
-++ obsolete [ "environment" "checkConfigurationOptions" ] [ "__internal" "check" ]
+++ obsolete [ "environment" "checkConfigurationOptions" ] [ "_module" "check" ]
 
 # Options that are obsolete and have no replacement.
 ++ obsolete' [ "boot" "loader" "grub" "bootDevice" ]
diff --git a/nixos/modules/services/misc/nixos-manual.nix b/nixos/modules/services/misc/nixos-manual.nix
index 72923f2b56a0..f73c4102cfe5 100644
--- a/nixos/modules/services/misc/nixos-manual.nix
+++ b/nixos/modules/services/misc/nixos-manual.nix
@@ -18,7 +18,7 @@ let
 
   eval = evalModules {
     modules = [ versionModule ] ++ baseModules;
-    args = (config.__internal.args) // { modules = [ ]; };
+    args = (config._module.args) // { modules = [ ]; };
   };
 
   manual = import ../../../doc/manual {