diff --git a/testing/web-platform/tests/encoding/api-basics.html b/testing/web-platform/tests/encoding/api-basics.html
index 084575655c9e..83670ce7dc3e 100644
--- a/testing/web-platform/tests/encoding/api-basics.html
+++ b/testing/web-platform/tests/encoding/api-basics.html
@@ -15,13 +15,11 @@ test(function() {
 }, 'Default inputs');
 
 
-function testEncodeDecodeSample(encoding, string, bytes) {
+function testDecodeSample(encoding, string, bytes) {
   test(function() {
-    var encoded = new TextEncoder(encoding).encode(string);
-    assert_array_equals([].slice.call(encoded), bytes);
     assert_equals(new TextDecoder(encoding).decode(new Uint8Array(bytes)), string);
     assert_equals(new TextDecoder(encoding).decode(new Uint8Array(bytes).buffer), string);
-  }, 'Encode/decode round trip: ' + encoding);
+  }, 'Decode sample: ' + encoding);
 }
 
 // z (ASCII U+007A), cent (Latin-1 U+00A2), CJK water (BMP U+6C34),
@@ -29,25 +27,29 @@ function testEncodeDecodeSample(encoding, string, bytes) {
 // byte-swapped BOM (non-character U+FFFE)
 var sample = 'z\xA2\u6C34\uD834\uDD1E\uF8FF\uDBFF\uDFFD\uFFFE';
 
-testEncodeDecodeSample(
-  'utf-8',
-  sample,
-  [0x7A, 0xC2, 0xA2, 0xE6, 0xB0, 0xB4, 0xF0, 0x9D, 0x84, 0x9E, 0xEF, 0xA3, 0xBF, 0xF4, 0x8F, 0xBF, 0xBD, 0xEF, 0xBF, 0xBE]
-);
+test(function() {
+  var encoding = 'utf-8';
+  var string = sample;
+  var bytes = [0x7A, 0xC2, 0xA2, 0xE6, 0xB0, 0xB4, 0xF0, 0x9D, 0x84, 0x9E, 0xEF, 0xA3, 0xBF, 0xF4, 0x8F, 0xBF, 0xBD, 0xEF, 0xBF, 0xBE];
+  var encoded = new TextEncoder().encode(string);
+  assert_array_equals([].slice.call(encoded), bytes);
+  assert_equals(new TextDecoder(encoding).decode(new Uint8Array(bytes)), string);
+  assert_equals(new TextDecoder(encoding).decode(new Uint8Array(bytes).buffer), string);
+}, 'Encode/decode round trip: utf-8');
 
-testEncodeDecodeSample(
+testDecodeSample(
   'utf-16le',
   sample,
   [0x7A, 0x00, 0xA2, 0x00, 0x34, 0x6C, 0x34, 0xD8, 0x1E, 0xDD, 0xFF, 0xF8, 0xFF, 0xDB, 0xFD, 0xDF, 0xFE, 0xFF]
 );
 
-testEncodeDecodeSample(
+testDecodeSample(
   'utf-16be',
   sample,
   [0x00, 0x7A, 0x00, 0xA2, 0x6C, 0x34, 0xD8, 0x34, 0xDD, 0x1E, 0xF8, 0xFF, 0xDB, 0xFF, 0xDF, 0xFD, 0xFF, 0xFE]
 );
 
-testEncodeDecodeSample(
+testDecodeSample(
   'utf-16',
   sample,
   [0x7A, 0x00, 0xA2, 0x00, 0x34, 0x6C, 0x34, 0xD8, 0x1E, 0xDD, 0xFF, 0xF8, 0xFF, 0xDB, 0xFD, 0xDF, 0xFE, 0xFF]
diff --git a/testing/web-platform/tests/encoding/api-invalid-label.html b/testing/web-platform/tests/encoding/api-invalid-label.html
index ff037173a112..f15c184aa897 100644
--- a/testing/web-platform/tests/encoding/api-invalid-label.html
+++ b/testing/web-platform/tests/encoding/api-invalid-label.html
@@ -23,10 +23,6 @@ setup(function() {
 });
 
 tests.forEach(function(input) {
-  test(function() {
-    assert_throws(new RangeError(), function() { new TextEncoder(input); });
-  }, 'Invalid label ' + format_value(input) + ' should be rejected by TextEncoder.');
-
   test(function() {
     assert_throws(new RangeError(), function() { new TextDecoder(input); });
   }, 'Invalid label ' + format_value(input) + ' should be rejected by TextDecoder.');
diff --git a/testing/web-platform/tests/encoding/api-replacement-encodings.html b/testing/web-platform/tests/encoding/api-replacement-encodings.html
index ef0cdb88ec00..2dffd72e7b48 100644
--- a/testing/web-platform/tests/encoding/api-replacement-encodings.html
+++ b/testing/web-platform/tests/encoding/api-replacement-encodings.html
@@ -6,7 +6,6 @@
 <script>
 
 test(function() {
-    assert_throws(new RangeError(), function() { new TextEncoder('replacement'); });
     assert_throws(new RangeError(), function() { new TextDecoder('replacement'); });
 }, 'The "replacement" label should not be a known encoding.');
 
@@ -16,7 +15,6 @@ encodings_table.forEach(function(section) {
     }).forEach(function(encoding) {
         encoding.labels.forEach(function(label) {
             test(function() {
-                assert_throws(new RangeError(), function() { new TextEncoder(label); });
                 assert_throws(new RangeError(), function() { new TextDecoder(label); });
             }, 'Label for "replacement" should be rejected by API: ' + label);
         });
diff --git a/testing/web-platform/tests/encoding/idlharness.html b/testing/web-platform/tests/encoding/idlharness.html
index ce44f6d3e0b2..c010df3fafa3 100644
--- a/testing/web-platform/tests/encoding/idlharness.html
+++ b/testing/web-platform/tests/encoding/idlharness.html
@@ -38,7 +38,7 @@ interface TextDecoder {
 
 // 8.2 Interface TextDecoder
 
-[Constructor(optional DOMString utfLabel = "utf-8"),
+[Constructor,
  Exposed=Window,Worker]
 interface TextEncoder {
   readonly attribute DOMString encoding;
diff --git a/testing/web-platform/tests/encoding/textdecoder-streaming.html b/testing/web-platform/tests/encoding/textdecoder-streaming.html
index d514a1806482..211b3c00918c 100644
--- a/testing/web-platform/tests/encoding/textdecoder-streaming.html
+++ b/testing/web-platform/tests/encoding/textdecoder-streaming.html
@@ -5,12 +5,23 @@
 <script src="resources/encodings.js"></script>
 <script>
 
-var string = '\\x00123ABCabc\\x80\\xFF\\u0100\\u1000\\uFFFD\\uD800\\uDC00\\uDBFF\\uDFFF';
+var string = '\x00123ABCabc\x80\xFF\u0100\u1000\uFFFD\uD800\uDC00\uDBFF\uDFFF';
+var octets = {
+    'utf-16le': [0x00,0x00,0x31,0x00,0x32,0x00,0x33,0x00,0x41,0x00,0x42,0x00,
+                 0x43,0x00,0x61,0x00,0x62,0x00,0x63,0x00,0x80,0x00,0xFF,0x00,
+                 0x00,0x01,0x00,0x10,0xFD,0xFF,0x00,0xD8,0x00,0xDC,0xFF,0xDB,
+                 0xFF,0xDF],
+    'utf-16be': [0x00,0x00,0x00,0x31,0x00,0x32,0x00,0x33,0x00,0x41,0x00,0x42,
+                 0x00,0x43,0x00,0x61,0x00,0x62,0x00,0x63,0x00,0x80,0x00,0xFF,
+                 0x01,0x00,0x10,0x00,0xFF,0xFD,0xD8,0x00,0xDC,0x00,0xDB,0xFF,
+                 0xDF,0xFF]
+};
 
 utf_encodings.forEach(function (encoding) {
     for (var len = 1; len <= 5; ++len) {
         test(function() {
-            var encoded = new TextEncoder(encoding).encode(string);
+            var encoded = octets[encoding] ||
+                          new TextEncoder(encoding).encode(string);
 
             var out = '';
             var decoder = new TextDecoder(encoding);
diff --git a/testing/web-platform/tests/encoding/textencoder-constructor-non-utf.html b/testing/web-platform/tests/encoding/textencoder-constructor-non-utf.html
index 82ad56bc46f5..f5c2ea545091 100644
--- a/testing/web-platform/tests/encoding/textencoder-constructor-non-utf.html
+++ b/testing/web-platform/tests/encoding/textencoder-constructor-non-utf.html
@@ -6,20 +6,16 @@
 <script>
 
 encodings_table.forEach(function(section) {
-    section.encodings.filter(function(encoding) {
-        return encoding.name !== 'replacement';
-    }).forEach(function(encoding) {
-        if (utf_encodings.indexOf(encoding.name) !== -1) {
+    section.encodings.forEach(function(encoding) {
+        if (encoding.name !== 'replacement') {
             test(function() {
                 assert_equals(new TextDecoder(encoding.name).encoding, encoding.name);
-                assert_equals(new TextEncoder(encoding.name).encoding, encoding.name);
-            }, 'UTF encodings are supported for encode and decode: ' + encoding.name);
-        } else {
-            test(function() {
-                assert_equals(new TextDecoder(encoding.name).encoding, encoding.name);
-                assert_throws(new RangeError(), function() { new TextEncoder(encoding.name); });
-            }, 'Non-UTF encodings supported only for decode, not encode: ' + encoding.name);
+            }, 'Encoding argument supported for decode: ' + encoding.name);
         }
+
+        test(function() {
+            assert_equals(new TextEncoder(encoding.name).encoding, 'utf-8');
+        }, 'Encoding argument not considered for encode: ' + encoding.name);
     });
 });