diff --git a/harness/features.yml b/harness/features.yml
index 177bec32bd..d08adaf646 100644
--- a/harness/features.yml
+++ b/harness/features.yml
@@ -1,3 +1,4 @@
 typeCoercion.js: [Symbol.toPrimitive, BigInt]
 testAtomics.js: [ArrayBuffer, Atomics, DataView, SharedArrayBuffer, arrow-function, let, for-of]
 testTypedArray.js: [TypedArray]
+isConstructor.js: [Reflect.construct]
diff --git a/harness/isConstructor.js b/harness/isConstructor.js
new file mode 100644
index 0000000000..bf7433219e
--- /dev/null
+++ b/harness/isConstructor.js
@@ -0,0 +1,16 @@
+// Copyright (C) 2017 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: |
+    Test if a given function is a constructor function.
+---*/
+
+function isConstructor(f) {
+    try {
+        Reflect.construct(function(){}, [], f);
+    } catch (e) {
+        return false;
+    }
+    return true;
+}
diff --git a/test/intl402/Collator/prototype/compare/10.3.2_1_a_L15.js b/test/intl402/Collator/prototype/compare/10.3.2_1_a_L15.js
index db72d12a29..0d40250aff 100644
--- a/test/intl402/Collator/prototype/compare/10.3.2_1_a_L15.js
+++ b/test/intl402/Collator/prototype/compare/10.3.2_1_a_L15.js
@@ -9,7 +9,22 @@ description: >
     built-in objects defined by the introduction of chapter 17 of the
     ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(new Intl.Collator().compare);
+var compareFn = new Intl.Collator().compare;
+
+assert.sameValue(Object.prototype.toString.call(compareFn), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(compareFn),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(compareFn), Function.prototype);
+
+assert.sameValue(compareFn.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(compareFn), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/Collator/prototype/compare/10.3.2_L15.js b/test/intl402/Collator/prototype/compare/10.3.2_L15.js
index 7f02924559..ab12bd28d4 100644
--- a/test/intl402/Collator/prototype/compare/10.3.2_L15.js
+++ b/test/intl402/Collator/prototype/compare/10.3.2_L15.js
@@ -8,7 +8,22 @@ description: >
     the requirements for built-in objects defined by the introduction
     of chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Object.getOwnPropertyDescriptor(Intl.Collator.prototype, "compare").get);
+var compareFn = Object.getOwnPropertyDescriptor(Intl.Collator.prototype, "compare").get;
+
+assert.sameValue(Object.prototype.toString.call(compareFn), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(compareFn),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(compareFn), Function.prototype);
+
+assert.sameValue(compareFn.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(compareFn), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/Collator/prototype/resolvedOptions/10.3.3_L15.js b/test/intl402/Collator/prototype/resolvedOptions/10.3.3_L15.js
index 51cfef46c4..cf83b0a628 100644
--- a/test/intl402/Collator/prototype/resolvedOptions/10.3.3_L15.js
+++ b/test/intl402/Collator/prototype/resolvedOptions/10.3.3_L15.js
@@ -8,7 +8,20 @@ description: >
     requirements for built-in objects defined by the introduction of
     chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Intl.Collator.prototype.resolvedOptions);
+assert.sameValue(Object.prototype.toString.call(Intl.Collator.prototype.resolvedOptions), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Intl.Collator.prototype.resolvedOptions),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Intl.Collator.prototype.resolvedOptions), Function.prototype);
+
+assert.sameValue(Intl.Collator.prototype.resolvedOptions.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Intl.Collator.prototype.resolvedOptions), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/Collator/supportedLocalesOf/10.2.2_L15.js b/test/intl402/Collator/supportedLocalesOf/10.2.2_L15.js
index 61e057c6ac..8fc4a24d46 100644
--- a/test/intl402/Collator/supportedLocalesOf/10.2.2_L15.js
+++ b/test/intl402/Collator/supportedLocalesOf/10.2.2_L15.js
@@ -8,7 +8,20 @@ description: >
     requirements for built-in objects defined by the introduction of
     chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Intl.Collator.supportedLocalesOf);
+assert.sameValue(Object.prototype.toString.call(Intl.Collator.supportedLocalesOf), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Intl.Collator.supportedLocalesOf),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Intl.Collator.supportedLocalesOf), Function.prototype);
+
+assert.sameValue(Intl.Collator.supportedLocalesOf.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Intl.Collator.supportedLocalesOf), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/Date/prototype/toLocaleDateString/13.3.2_L15.js b/test/intl402/Date/prototype/toLocaleDateString/13.3.2_L15.js
index c8c9a939da..70b8b9d796 100644
--- a/test/intl402/Date/prototype/toLocaleDateString/13.3.2_L15.js
+++ b/test/intl402/Date/prototype/toLocaleDateString/13.3.2_L15.js
@@ -8,7 +8,20 @@ description: >
     requirements for built-in objects defined by the introduction of
     chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Date.prototype.toLocaleDateString);
+assert.sameValue(Object.prototype.toString.call(Date.prototype.toLocaleDateString), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Date.prototype.toLocaleDateString),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Date.prototype.toLocaleDateString), Function.prototype);
+
+assert.sameValue(Date.prototype.toLocaleDateString.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Date.prototype.toLocaleDateString), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/Date/prototype/toLocaleString/13.3.1_L15.js b/test/intl402/Date/prototype/toLocaleString/13.3.1_L15.js
index d22b9ad9d1..dde2899d21 100644
--- a/test/intl402/Date/prototype/toLocaleString/13.3.1_L15.js
+++ b/test/intl402/Date/prototype/toLocaleString/13.3.1_L15.js
@@ -8,7 +8,20 @@ description: >
     for built-in objects defined by the introduction of chapter 17 of
     the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Date.prototype.toLocaleString);
+assert.sameValue(Object.prototype.toString.call(Date.prototype.toLocaleString), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Date.prototype.toLocaleString),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Date.prototype.toLocaleString), Function.prototype);
+
+assert.sameValue(Date.prototype.toLocaleString.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Date.prototype.toLocaleString), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/Date/prototype/toLocaleTimeString/13.3.3_L15.js b/test/intl402/Date/prototype/toLocaleTimeString/13.3.3_L15.js
index 4064f756d8..5e61e709d2 100644
--- a/test/intl402/Date/prototype/toLocaleTimeString/13.3.3_L15.js
+++ b/test/intl402/Date/prototype/toLocaleTimeString/13.3.3_L15.js
@@ -8,7 +8,20 @@ description: >
     requirements for built-in objects defined by the introduction of
     chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Date.prototype.toLocaleTimeString);
+assert.sameValue(Object.prototype.toString.call(Date.prototype.toLocaleTimeString), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Date.prototype.toLocaleTimeString),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Date.prototype.toLocaleTimeString), Function.prototype);
+
+assert.sameValue(Date.prototype.toLocaleTimeString.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Date.prototype.toLocaleTimeString), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/DateTimeFormat/prototype/format/12.3.2_1_a_L15.js b/test/intl402/DateTimeFormat/prototype/format/12.3.2_1_a_L15.js
index 42facb22d1..4fa4f3e6b0 100644
--- a/test/intl402/DateTimeFormat/prototype/format/12.3.2_1_a_L15.js
+++ b/test/intl402/DateTimeFormat/prototype/format/12.3.2_1_a_L15.js
@@ -9,7 +9,22 @@ description: >
     built-in objects defined by the introduction of chapter 17 of the
     ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(new Intl.DateTimeFormat().format);
+var formatFn = new Intl.DateTimeFormat().format;
+
+assert.sameValue(Object.prototype.toString.call(formatFn), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(formatFn),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(formatFn), Function.prototype);
+
+assert.sameValue(formatFn.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(formatFn), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/DateTimeFormat/prototype/format/12.3.2_L15.js b/test/intl402/DateTimeFormat/prototype/format/12.3.2_L15.js
index 280ca055f5..f0862c45c1 100644
--- a/test/intl402/DateTimeFormat/prototype/format/12.3.2_L15.js
+++ b/test/intl402/DateTimeFormat/prototype/format/12.3.2_L15.js
@@ -9,7 +9,22 @@ description: >
     introduction of chapter 17 of the ECMAScript Language
     Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Object.getOwnPropertyDescriptor(Intl.DateTimeFormat.prototype, "format").get);
+var formatFn = Object.getOwnPropertyDescriptor(Intl.DateTimeFormat.prototype, "format").get;
+
+assert.sameValue(Object.prototype.toString.call(formatFn), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(formatFn),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(formatFn), Function.prototype);
+
+assert.sameValue(formatFn.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(formatFn), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/DateTimeFormat/prototype/resolvedOptions/12.3.3_L15.js b/test/intl402/DateTimeFormat/prototype/resolvedOptions/12.3.3_L15.js
index 8a9f5db478..db4e3b9f5b 100644
--- a/test/intl402/DateTimeFormat/prototype/resolvedOptions/12.3.3_L15.js
+++ b/test/intl402/DateTimeFormat/prototype/resolvedOptions/12.3.3_L15.js
@@ -8,7 +8,20 @@ description: >
     the requirements for built-in objects defined by the introduction
     of chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Intl.DateTimeFormat.prototype.resolvedOptions);
+assert.sameValue(Object.prototype.toString.call(Intl.DateTimeFormat.prototype.resolvedOptions), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Intl.DateTimeFormat.prototype.resolvedOptions),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Intl.DateTimeFormat.prototype.resolvedOptions), Function.prototype);
+
+assert.sameValue(Intl.DateTimeFormat.prototype.resolvedOptions.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Intl.DateTimeFormat.prototype.resolvedOptions), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/DateTimeFormat/supportedLocalesOf/12.2.2_L15.js b/test/intl402/DateTimeFormat/supportedLocalesOf/12.2.2_L15.js
index 6ead0ebc8a..d67b64bfca 100644
--- a/test/intl402/DateTimeFormat/supportedLocalesOf/12.2.2_L15.js
+++ b/test/intl402/DateTimeFormat/supportedLocalesOf/12.2.2_L15.js
@@ -8,7 +8,20 @@ description: >
     requirements for built-in objects defined by the introduction of
     chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Intl.DateTimeFormat.supportedLocalesOf);
+assert.sameValue(Object.prototype.toString.call(Intl.DateTimeFormat.supportedLocalesOf), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Intl.DateTimeFormat.supportedLocalesOf),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Intl.DateTimeFormat.supportedLocalesOf), Function.prototype);
+
+assert.sameValue(Intl.DateTimeFormat.supportedLocalesOf.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Intl.DateTimeFormat.supportedLocalesOf), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/Number/prototype/toLocaleString/13.2.1_L15.js b/test/intl402/Number/prototype/toLocaleString/13.2.1_L15.js
index 6858f76d26..5e5ece0f17 100644
--- a/test/intl402/Number/prototype/toLocaleString/13.2.1_L15.js
+++ b/test/intl402/Number/prototype/toLocaleString/13.2.1_L15.js
@@ -8,7 +8,20 @@ description: >
     for built-in objects defined by the introduction of chapter 17 of
     the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Number.prototype.toLocaleString);
+assert.sameValue(Object.prototype.toString.call(Number.prototype.toLocaleString), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Number.prototype.toLocaleString),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Number.prototype.toLocaleString), Function.prototype);
+
+assert.sameValue(Number.prototype.toLocaleString.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Number.prototype.toLocaleString), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/NumberFormat/prototype/format/11.3.2_1_a_L15.js b/test/intl402/NumberFormat/prototype/format/11.3.2_1_a_L15.js
index 827b7d6fea..d7efa612a2 100644
--- a/test/intl402/NumberFormat/prototype/format/11.3.2_1_a_L15.js
+++ b/test/intl402/NumberFormat/prototype/format/11.3.2_1_a_L15.js
@@ -9,7 +9,22 @@ description: >
     built-in objects defined by the introduction of chapter 17 of the
     ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(new Intl.NumberFormat().format);
+var formatFn = new Intl.NumberFormat().format;
+
+assert.sameValue(Object.prototype.toString.call(formatFn), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(formatFn),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(formatFn), Function.prototype);
+
+assert.sameValue(formatFn.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(formatFn), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/NumberFormat/prototype/format/11.3.2_L15.js b/test/intl402/NumberFormat/prototype/format/11.3.2_L15.js
index 8850dc0cb7..c89a62c6e5 100644
--- a/test/intl402/NumberFormat/prototype/format/11.3.2_L15.js
+++ b/test/intl402/NumberFormat/prototype/format/11.3.2_L15.js
@@ -9,7 +9,22 @@ description: >
     introduction of chapter 17 of the ECMAScript Language
     Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Object.getOwnPropertyDescriptor(Intl.NumberFormat.prototype, "format").get);
+var formatFn = Object.getOwnPropertyDescriptor(Intl.NumberFormat.prototype, "format").get;
+
+assert.sameValue(Object.prototype.toString.call(formatFn), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(formatFn),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(formatFn), Function.prototype);
+
+assert.sameValue(formatFn.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(formatFn), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/NumberFormat/prototype/resolvedOptions/11.3.3_L15.js b/test/intl402/NumberFormat/prototype/resolvedOptions/11.3.3_L15.js
index 237aae7595..02c99d7349 100644
--- a/test/intl402/NumberFormat/prototype/resolvedOptions/11.3.3_L15.js
+++ b/test/intl402/NumberFormat/prototype/resolvedOptions/11.3.3_L15.js
@@ -8,7 +8,20 @@ description: >
     requirements for built-in objects defined by the introduction of
     chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Intl.NumberFormat.prototype.resolvedOptions);
+assert.sameValue(Object.prototype.toString.call(Intl.NumberFormat.prototype.resolvedOptions), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Intl.NumberFormat.prototype.resolvedOptions),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Intl.NumberFormat.prototype.resolvedOptions), Function.prototype);
+
+assert.sameValue(Intl.NumberFormat.prototype.resolvedOptions.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Intl.NumberFormat.prototype.resolvedOptions), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/NumberFormat/supportedLocalesOf/11.2.2_L15.js b/test/intl402/NumberFormat/supportedLocalesOf/11.2.2_L15.js
index c3c362e56d..64a3869eaa 100644
--- a/test/intl402/NumberFormat/supportedLocalesOf/11.2.2_L15.js
+++ b/test/intl402/NumberFormat/supportedLocalesOf/11.2.2_L15.js
@@ -8,7 +8,20 @@ description: >
     requirements for built-in objects defined by the introduction of
     chapter 17 of the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Intl.NumberFormat.supportedLocalesOf);
+assert.sameValue(Object.prototype.toString.call(Intl.NumberFormat.supportedLocalesOf), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Intl.NumberFormat.supportedLocalesOf),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Intl.NumberFormat.supportedLocalesOf), Function.prototype);
+
+assert.sameValue(Intl.NumberFormat.supportedLocalesOf.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Intl.NumberFormat.supportedLocalesOf), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/PluralRules/prototype/resolvedOptions/builtins.js b/test/intl402/PluralRules/prototype/resolvedOptions/builtins.js
index 2649acf106..e25ff3caa7 100644
--- a/test/intl402/PluralRules/prototype/resolvedOptions/builtins.js
+++ b/test/intl402/PluralRules/prototype/resolvedOptions/builtins.js
@@ -8,7 +8,20 @@ description: >
     built-in objects defined by the introduction of chapter 17 of the
     ECMAScript Language Specification.
 author: Zibi Braniecki
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Intl.PluralRules.prototype.resolvedOptions);
+assert.sameValue(Object.prototype.toString.call(Intl.PluralRules.prototype.resolvedOptions), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Intl.PluralRules.prototype.resolvedOptions),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Intl.PluralRules.prototype.resolvedOptions), Function.prototype);
+
+assert.sameValue(Intl.PluralRules.prototype.resolvedOptions.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Intl.PluralRules.prototype.resolvedOptions), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/PluralRules/supportedLocalesOf/supportedLocalesOf.js b/test/intl402/PluralRules/supportedLocalesOf/supportedLocalesOf.js
index cbee32b4b3..ee6984f652 100644
--- a/test/intl402/PluralRules/supportedLocalesOf/supportedLocalesOf.js
+++ b/test/intl402/PluralRules/supportedLocalesOf/supportedLocalesOf.js
@@ -8,7 +8,20 @@ description: >
     built-in objects defined by the introduction of chapter 17 of the
     ECMAScript Language Specification.
 author: Zibi Braniecki
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(Intl.PluralRules.supportedLocalesOf);
+assert.sameValue(Object.prototype.toString.call(Intl.PluralRules.supportedLocalesOf), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(Intl.PluralRules.supportedLocalesOf),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(Intl.PluralRules.supportedLocalesOf), Function.prototype);
+
+assert.sameValue(Intl.PluralRules.supportedLocalesOf.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(Intl.PluralRules.supportedLocalesOf), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");
diff --git a/test/intl402/String/prototype/localeCompare/13.1.1_L15.js b/test/intl402/String/prototype/localeCompare/13.1.1_L15.js
index d7cfdff794..67db4ed5a3 100644
--- a/test/intl402/String/prototype/localeCompare/13.1.1_L15.js
+++ b/test/intl402/String/prototype/localeCompare/13.1.1_L15.js
@@ -8,7 +8,20 @@ description: >
     for built-in objects defined by the introduction of chapter 17 of
     the ECMAScript Language Specification.
 author: Norbert Lindenberg
-includes: [testBuiltInObject.js]
+includes: [isConstructor.js]
 ---*/
 
-testBuiltInObject(String.prototype.localeCompare);
+assert.sameValue(Object.prototype.toString.call(String.prototype.localeCompare), "[object Function]",
+                 "The [[Class]] internal property of a built-in function must be " +
+                 "\"Function\".");
+
+assert(Object.isExtensible(String.prototype.localeCompare),
+       "Built-in objects must be extensible.");
+
+assert.sameValue(Object.getPrototypeOf(String.prototype.localeCompare), Function.prototype);
+
+assert.sameValue(String.prototype.localeCompare.hasOwnProperty("prototype"), false,
+                 "Built-in functions that aren't constructors must not have a prototype property.");
+
+assert.sameValue(isConstructor(String.prototype.localeCompare), false,
+                 "Built-in functions don't implement [[Construct]] unless explicitly specified.");