diff --git a/jerry-core/ecma/builtin-objects/ecma-builtins.c b/jerry-core/ecma/builtin-objects/ecma-builtins.c
index 3ede40ee0..730353675 100644
--- a/jerry-core/ecma/builtin-objects/ecma-builtins.c
+++ b/jerry-core/ecma/builtin-objects/ecma-builtins.c
@@ -650,17 +650,32 @@ ecma_builtin_try_to_instantiate_property (ecma_object_t *object_p, /**< object *
     {
       /*
        * Lazy instantiation of 'length' property
-       *
-       * Note:
-       *      We don't need to mark that the property was already lazy instantiated,
-       *      as it is non-configurable and so can't be deleted
        */
 
       ecma_property_t *len_prop_p;
+#if ENABLED (JERRY_ES2015)
+      ecma_extended_object_t *ext_func_p = (ecma_extended_object_t *) object_p;
+      uint32_t *bitset_p = ext_func_p->u.built_in.instantiated_bitset;
+      if (*bitset_p & (1u << 0))
+      {
+        /* length property was already instantiated */
+        return NULL;
+      }
+      /* We mark that the property was lazily instantiated,
+       * as it is configurable and so can be deleted (ECMA-262 v6, 19.2.4.1) */
+      *bitset_p |= (1u << 0);
+      ecma_property_value_t *len_prop_value_p = ecma_create_named_data_property (object_p,
+                                                                                 string_p,
+                                                                                 ECMA_PROPERTY_FLAG_CONFIGURABLE,
+                                                                                 &len_prop_p);
+#else /* !ENABLED (JERRY_ES2015) */
+      /* We don't need to mark that the property was already lazy instantiated,
+       * as it is non-configurable and so can't be deleted (ECMA-262 v5, 13.2.5) */
       ecma_property_value_t *len_prop_value_p = ecma_create_named_data_property (object_p,
                                                                                  string_p,
                                                                                  ECMA_PROPERTY_FIXED,
                                                                                  &len_prop_p);
+#endif /* ENABLED (JERRY_ES2015) */
 
       ecma_extended_object_t *ext_obj_p = (ecma_extended_object_t *) object_p;
 
@@ -949,8 +964,17 @@ ecma_builtin_list_lazy_property_names (ecma_object_t *object_p, /**< a built-in
 
     if (!is_array_indices_only)
     {
+#if ENABLED (JERRY_ES2015)
+      ecma_extended_object_t *ext_func_p = (ecma_extended_object_t *) object_p;
+      if (!(ext_func_p->u.built_in.instantiated_bitset[0] & (1u << 0)))
+      {
+        /* Unintialized 'length' property is non-enumerable (ECMA-262 v6, 19.2.4.1) */
+        ecma_collection_push_back (for_non_enumerable_p, ecma_make_magic_string_value (LIT_MAGIC_STRING_LENGTH));
+      }
+#else /* !ENABLED (JERRY_ES2015) */
       /* 'length' property is non-enumerable (ECMA-262 v5, 15) */
       ecma_collection_push_back (for_non_enumerable_p, ecma_make_magic_string_value (LIT_MAGIC_STRING_LENGTH));
+#endif /* ENABLED (JERRY_ES2015) */
     }
   }
   else
diff --git a/tests/jerry-test-suite/es2015/15.03.04.02-001.js b/tests/jerry-test-suite/es2015/15.03.04.02-001.js
new file mode 100644
index 000000000..bf15596d6
--- /dev/null
+++ b/tests/jerry-test-suite/es2015/15.03.04.02-001.js
@@ -0,0 +1,17 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+assert(Function.prototype.toString.hasOwnProperty('length'));
+assert(delete Function.prototype.toString.length);
+assert(!Function.prototype.toString.hasOwnProperty('length'));
diff --git a/tests/jerry-test-suite/es2015/15.03.04.02-004.js b/tests/jerry-test-suite/es2015/15.03.04.02-004.js
new file mode 100644
index 000000000..bf15596d6
--- /dev/null
+++ b/tests/jerry-test-suite/es2015/15.03.04.02-004.js
@@ -0,0 +1,17 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+assert(Function.prototype.toString.hasOwnProperty('length'));
+assert(delete Function.prototype.toString.length);
+assert(!Function.prototype.toString.hasOwnProperty('length'));
diff --git a/tests/jerry-test-suite/15/15.03/15.03.04/15.03.04.02/15.03.04.02-001.js b/tests/jerry-test-suite/es5.1/15.03.04.02-001.js
similarity index 100%
rename from tests/jerry-test-suite/15/15.03/15.03.04/15.03.04.02/15.03.04.02-001.js
rename to tests/jerry-test-suite/es5.1/15.03.04.02-001.js
diff --git a/tests/jerry-test-suite/15/15.03/15.03.04/15.03.04.02/15.03.04.02-004.js b/tests/jerry-test-suite/es5.1/15.03.04.02-004.js
similarity index 100%
rename from tests/jerry-test-suite/15/15.03/15.03.04/15.03.04.02/15.03.04.02-004.js
rename to tests/jerry-test-suite/es5.1/15.03.04.02-004.js
diff --git a/tests/jerry/es2015/length-property.js b/tests/jerry/es2015/length-property.js
index 95937d83f..5a9230a1c 100644
--- a/tests/jerry/es2015/length-property.js
+++ b/tests/jerry/es2015/length-property.js
@@ -39,8 +39,6 @@ var builtin_objects = [
   WeakSet,
 ];
 
-var builtin_prototypes = [Function.prototype]
-
 var builtin_typedArrays = [
   Float32Array,
   Float64Array,
@@ -65,13 +63,6 @@ var builtin_typedArrays = [
     assert(desc.configurable === true);
   }
   
-  for (proto of builtin_prototypes) {
-    desc = Object.getOwnPropertyDescriptor(proto, 'length');                                                                                                                    
-    assert(desc.writable === false);
-    assert(desc.enumerable === false);
-    assert(desc.configurable === true);
-  }
-  
   for (ta of builtin_typedArrays) {
     desc = Object.getOwnPropertyDescriptor(ta, 'length');                                                                                                                    
     assert(desc.writable === false);
@@ -88,12 +79,6 @@ var builtin_typedArrays = [
     assert(obj.hasOwnProperty('length') === false);
   }
 
-  for (proto of builtin_prototypes) {
-    assert(proto.hasOwnProperty('length') === true);
-    assert(delete proto.length);
-    assert(proto.hasOwnProperty('length') === false);
-  }
-
   for (ta of builtin_typedArrays) {
     assert(ta.hasOwnProperty('length') === true);
     assert(delete ta.length);
@@ -101,6 +86,26 @@ var builtin_typedArrays = [
   }
 })();
 
+(function () {
+  /* test length property of builtin function */
+  for (obj of builtin_objects) {
+    var property_names = Object.getOwnPropertyNames(obj);
+    for (var name of property_names) {
+      if (typeof obj[name] == 'function') {
+        var func = obj[name];
+        var desc = Object.getOwnPropertyDescriptor(func, 'length');
+        assert(desc.writable === false);
+        assert(desc.enumerable === false);
+        assert(desc.configurable === true);
+
+        assert(func.hasOwnProperty('length') === true);
+        assert(delete func.length);
+        assert(func.hasOwnProperty('length') === false);
+      }
+    }
+  }
+})();
+
 (function () {
   /* test length property of function objects */
   var normal_func = function () {};
diff --git a/tests/jerry/string-prototype-charat.js b/tests/jerry/string-prototype-charat.js
index 68daf68b8..7c6698421 100644
--- a/tests/jerry/string-prototype-charat.js
+++ b/tests/jerry/string-prototype-charat.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.charAt, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.charAt, 'length').configurable === length_configurable());
 
 assert(Object.getOwnPropertyDescriptor(String.prototype.charAt, 'length').enumerable === false);
 
diff --git a/tests/jerry/string-prototype-charcodeat.js b/tests/jerry/string-prototype-charcodeat.js
index bfb68f635..35ff6ba34 100644
--- a/tests/jerry/string-prototype-charcodeat.js
+++ b/tests/jerry/string-prototype-charcodeat.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.charCodeAt, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.charCodeAt, 'length').configurable === length_configurable());
 
 assert(Object.getOwnPropertyDescriptor(String.prototype.charCodeAt, 'length').enumerable === false);
 
diff --git a/tests/jerry/string-prototype-concat.js b/tests/jerry/string-prototype-concat.js
index c00190341..5d4fc07a0 100644
--- a/tests/jerry/string-prototype-concat.js
+++ b/tests/jerry/string-prototype-concat.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.concat, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.concat, 'length').configurable === length_configurable());
 
 assert(Object.getOwnPropertyDescriptor(String.prototype.concat, 'length').enumerable === false);
 
diff --git a/tests/jerry/string-prototype-indexof.js b/tests/jerry/string-prototype-indexof.js
index a0b55fb43..f7ee266af 100644
--- a/tests/jerry/string-prototype-indexof.js
+++ b/tests/jerry/string-prototype-indexof.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.indexOf, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.indexOf, 'length').configurable === length_configurable());
 
 assert(Object.getOwnPropertyDescriptor(String.prototype.indexOf, 'length').enumerable === false);
 
diff --git a/tests/jerry/string-prototype-lastindexof.js b/tests/jerry/string-prototype-lastindexof.js
index ca90a7829..5ff0f0bc4 100644
--- a/tests/jerry/string-prototype-lastindexof.js
+++ b/tests/jerry/string-prototype-lastindexof.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.lastIndexOf, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.lastIndexOf, 'length').configurable === length_configurable());
 
 assert(Object.getOwnPropertyDescriptor(String.prototype.lastIndexOf, 'length').enumerable === false);
 
diff --git a/tests/jerry/string-prototype-match.js b/tests/jerry/string-prototype-match.js
index c8a099963..5318d2a3c 100644
--- a/tests/jerry/string-prototype-match.js
+++ b/tests/jerry/string-prototype-match.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.match, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.match, 'length').configurable === length_configurable());
 assert(Object.getOwnPropertyDescriptor(String.prototype.match, 'length').enumerable === false);
 assert(Object.getOwnPropertyDescriptor(String.prototype.match, 'length').writable === false);
 
diff --git a/tests/jerry/string-prototype-substr.js b/tests/jerry/string-prototype-substr.js
index 40613b7ff..1e4a662c5 100644
--- a/tests/jerry/string-prototype-substr.js
+++ b/tests/jerry/string-prototype-substr.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.substr, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.substr, 'length').configurable === length_configurable());
 
 assert(Object.getOwnPropertyDescriptor(String.prototype.substr, 'length').enumerable === false);
 
diff --git a/tests/jerry/string-prototype-substring.js b/tests/jerry/string-prototype-substring.js
index 51d03b1b0..78bda200d 100644
--- a/tests/jerry/string-prototype-substring.js
+++ b/tests/jerry/string-prototype-substring.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.substring, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.substring, 'length').configurable === length_configurable());
 
 assert(Object.getOwnPropertyDescriptor(String.prototype.substring, 'length').enumerable === false);
 
diff --git a/tests/jerry/string-prototype-trim.js b/tests/jerry/string-prototype-trim.js
index abeb31c74..2750e0ce2 100644
--- a/tests/jerry/string-prototype-trim.js
+++ b/tests/jerry/string-prototype-trim.js
@@ -13,7 +13,17 @@
 // limitations under the License.
 
 // check properties
-assert(Object.getOwnPropertyDescriptor(String.prototype.trim, 'length').configurable === false);
+
+function length_configurable()
+{
+  function is_es51() {
+    return (typeof g === "function");
+    { function g() {} }
+  }
+  return is_es51() ? false : true;
+}
+
+assert(Object.getOwnPropertyDescriptor(String.prototype.trim, 'length').configurable === length_configurable());
 
 assert(Object.getOwnPropertyDescriptor(String.prototype.trim, 'length').enumerable === false);