diff --git a/pkgs/lib/options.nix b/pkgs/lib/options.nix
index a7d1a3483a0..620de84e707 100644
--- a/pkgs/lib/options.nix
+++ b/pkgs/lib/options.nix
@@ -11,10 +11,10 @@ with import ./properties.nix;
 
 rec {
 
-  inherit (lib) isType;
+  inherit (lib) typeOf;
   
 
-  isOption = isType "option";
+  isOption = attrs: (typeOf attrs) == "option";
   mkOption = attrs: attrs // {
     _type = "option";
     # name (this is the name of the attributem it is automatically generated by the traversal)
@@ -190,7 +190,7 @@ rec {
             defValue = builtins.getAttr defName defs;
             optValue = builtins.getAttr defName opts;
           in
-          if isOption defValue
+          if typeOf defValue == "option"
           then
             # `defValue' is an option.
             if hasAttr defName opts
diff --git a/pkgs/lib/properties.nix b/pkgs/lib/properties.nix
index 22aa8d891d8..eeac27ae70c 100644
--- a/pkgs/lib/properties.nix
+++ b/pkgs/lib/properties.nix
@@ -11,13 +11,13 @@ with import ./attrsets.nix;
 
 rec {
 
-  inherit (lib) isType;
+  inherit (lib) typeOf;
 
   # Tell that nothing is defined.  When properties are evaluated, this type
   # is used to remove an entry.  Thus if your property evaluation semantic
   # implies that you have to mute the content of an attribute, then your
   # property should produce this value.
-  isNotdef = isType "notdef";
+  isNotdef = attrs: (typeOf attrs) == "notdef";
   mkNotdef = {_type = "notdef";};
 
   # General property type, it has a property attribute and a content
@@ -32,7 +32,7 @@ rec {
   #  - onGlobalDelay: run on all copied properties.
   #  - onEval: run on an evaluated property.
   #  - onGlobalEval: run on a list of property stack on top of their values.
-  isProperty = isType "property";
+  isProperty = attrs: (typeOf attrs) == "property";
   mkProperty = p@{property, content, ...}: p // {
     _type = "property";
   };
@@ -187,7 +187,7 @@ rec {
   # and interpreted by the underlying system using properties (modules).
 
   # Create a "Merge" property which only contains a condition.
-  isMerge = isType "merge";
+  isMerge = attrs: (typeOf attrs) == "merge";
   mkMerge = content: mkProperty {
     property = {
       _type = "merge";
@@ -204,7 +204,7 @@ rec {
   # is ignore.
 
   # Create a "If" property which only contains a condition.
-  isIf = isType "if";
+  isIf = attrs: (typeOf attrs) == "if";
   mkIf = condition: content: mkProperty {
     property = {
       _type = "if";
@@ -271,7 +271,7 @@ rec {
   # priorities between values.  The default priority is 100. The lowest
   # priorities are kept.  The template argument must reproduce the same
   # attribute set hierarchy to override leaves of the hierarchy.
-  isOverride = isType "override";
+  isOverride = attrs: (typeOf attrs) == "override";
   mkOverrideTemplate = priority: template: content: mkProperty {
     property = {
       _type = "override";
@@ -371,7 +371,7 @@ rec {
   # of the list used by the merge function.  And the highest ranked
   # definition would be the last.  Definitions which does not have any rank
   # value have the default rank of 100.
-  isOrder = isType "order";
+  isOrder = attrs: (typeOf attrs) == "order";
   mkOrder = rank: content: mkProperty {
     property = {
       _type = "order";
@@ -434,7 +434,7 @@ rec {
   # properties on top of the option definition is nice for user manipulation
   # but require to check if the content of the property is not another
   # property.  Such testing implies to verify if this is an attribute set
-  # and if it possess the type 'property'. (see isProperty & typeOf/isType)
+  # and if it possess the type 'property'. (see isProperty & typeOf)
   #
   # To avoid strict evaluation of option definitions, 'mkFixStrictness' is
   # introduced.  This property protects an option definition by replacing
diff --git a/pkgs/lib/systems.nix b/pkgs/lib/systems.nix
index 02c26ba600a..09d04042f1c 100644
--- a/pkgs/lib/systems.nix
+++ b/pkgs/lib/systems.nix
@@ -15,14 +15,14 @@ in
 
 rec {
 
-  isSignificantByte = isType "significant-byte";
+  isSignificantByte = x: typeOf x == "significant-byte";
   significantBytes = setTypes "significant-byte" {
     bigEndian = {};
     littleEndian = {};
   };
 
 
-  isCpuType = isType "cpu-type"
+  isCpuType = x: typeOf x == "cpu-type"
     && elem x.bits [8 16 32 64 128]
     && (builtins.lessThan 8 x.bits -> isSignificantByte x.significantByte);
 
@@ -37,7 +37,7 @@ rec {
     };
 
 
-  isExecFormat = isType "exec-format";
+  isExecFormat = x: typeOf x == "exec-format";
   execFormats = setTypes "exec-format" {
     aout = {}; # a.out
     elf = {};
@@ -47,7 +47,7 @@ rec {
   };
 
 
-  isKernel = isType "kernel";
+  isKernel = x: typeOf x == "kernel";
   kernels = with execFormats;
     setTypes "kernel" {
       cygwin =  { execFormat = pe; };
@@ -61,7 +61,7 @@ rec {
     };
 
 
-  isArchitecture = isType "architecture";
+  isArchitecture = x: typeOf x == "architecture";
   architectures = setTypes "architecture" {
     apple = {};
     pc = {};
@@ -69,7 +69,7 @@ rec {
   };
 
 
-  isSystem = isType "system"
+  isSystem = x: typeOf x == "system"
     && isCpuType x.cpu
     && isArchitecture x.arch
     && isKernel x.kernel;
diff --git a/pkgs/lib/types.nix b/pkgs/lib/types.nix
index 156d72ac5e7..9dce885b182 100644
--- a/pkgs/lib/types.nix
+++ b/pkgs/lib/types.nix
@@ -10,7 +10,6 @@ with import ./trivial.nix;
 
 rec {
 
-  isType = type: x: (x._type or "") == type;
   hasType = x: isAttrs x && x ? _type;
   typeOf = x: x._type or "";
 
@@ -27,7 +26,7 @@ rec {
   # hasOptions (boolean: whatever this option contains an option set)
   # delayOnGlobalEval (boolean: should properties go through the evaluation of this option)
   # docPath (path concatenated to the option name contained in the option set)
-  isOptionType = isType "option-type";
+  isOptionType = attrs: typeOf attrs == "option-type";
   mkOptionType =
     { name
     , check ? (x: true)