diff --git a/src/node_i18n.cc b/src/node_i18n.cc
index dc50f9995a695e..f35bf2685592a4 100644
--- a/src/node_i18n.cc
+++ b/src/node_i18n.cc
@@ -450,6 +450,9 @@ int32_t ToUnicode(MaybeStackBuffer<char>* buf,
                                         &info,
                                         &status);
 
+  // Do not check info.errors like we do with ToASCII since ToUnicode always
+  // returns a string, despite any possible errors that may have occurred.
+
   if (status == U_BUFFER_OVERFLOW_ERROR) {
     status = U_ZERO_ERROR;
     buf->AllocateSufficientStorage(len);
@@ -477,9 +480,18 @@ int32_t ToUnicode(MaybeStackBuffer<char>* buf,
 int32_t ToASCII(MaybeStackBuffer<char>* buf,
                 const char* input,
                 size_t length,
-                bool lenient) {
+                enum idna_mode mode) {
   UErrorCode status = U_ZERO_ERROR;
-  uint32_t options = UIDNA_NONTRANSITIONAL_TO_ASCII | UIDNA_CHECK_BIDI;
+  uint32_t options =                  // CheckHyphens = false; handled later
+    UIDNA_CHECK_BIDI |                // CheckBidi = true
+    UIDNA_CHECK_CONTEXTJ |            // CheckJoiners = true
+    UIDNA_NONTRANSITIONAL_TO_ASCII;   // Nontransitional_Processing
+  if (mode == IDNA_STRICT) {
+    options |= UIDNA_USE_STD3_RULES;  // UseSTD3ASCIIRules = beStrict
+                                      // VerifyDnsLength = beStrict;
+                                      //   handled later
+  }
+
   UIDNA* uidna = uidna_openUTS46(options, &status);
   if (U_FAILURE(status))
     return -1;
@@ -501,21 +513,17 @@ int32_t ToASCII(MaybeStackBuffer<char>* buf,
                                  &status);
   }
 
-  // The WHATWG URL "domain to ASCII" algorithm explicitly sets the
-  // VerifyDnsLength flag to false, which disables the domain name length
-  // verification step in ToASCII (as specified by UTS #46). Unfortunately,
-  // ICU4C's IDNA module does not support disabling this flag through `options`,
-  // so just filter out the errors that may be caused by the verification step
-  // afterwards.
-  info.errors &= ~UIDNA_ERROR_EMPTY_LABEL;
-  info.errors &= ~UIDNA_ERROR_LABEL_TOO_LONG;
-  info.errors &= ~UIDNA_ERROR_DOMAIN_NAME_TOO_LONG;
-
-  // These error conditions are mandated unconditionally by UTS #46 version
-  // 9.0.0 (rev. 17), but were found to be incompatible with actual domain
-  // names in the wild. As such, in the current UTS #46 draft (rev. 18) these
-  // checks are made optional depending on the CheckHyphens flag, which will be
-  // disabled in WHATWG URL's "domain to ASCII" algorithm soon.
+  // In UTS #46 which specifies ToASCII, certain error conditions are
+  // configurable through options, and the WHATWG URL Standard promptly elects
+  // to disable some of them to accomodate for real-world use cases.
+  // Unfortunately, ICU4C's IDNA module does not support disabling some of
+  // these options through `options` above, and thus continues throwing
+  // unnecessary errors. To counter this situation, we just filter out the
+  // errors that may have happened afterwards, before deciding whether to
+  // return an error from this function.
+
+  // CheckHyphens = false
+  // (Specified in the current UTS #46 draft rev. 18.)
   // Refs:
   // - https://github.com/whatwg/url/issues/53
   // - https://github.com/whatwg/url/pull/309
@@ -526,7 +534,14 @@ int32_t ToASCII(MaybeStackBuffer<char>* buf,
   info.errors &= ~UIDNA_ERROR_LEADING_HYPHEN;
   info.errors &= ~UIDNA_ERROR_TRAILING_HYPHEN;
 
-  if (U_FAILURE(status) || (!lenient && info.errors != 0)) {
+  if (mode != IDNA_STRICT) {
+    // VerifyDnsLength = beStrict
+    info.errors &= ~UIDNA_ERROR_EMPTY_LABEL;
+    info.errors &= ~UIDNA_ERROR_LABEL_TOO_LONG;
+    info.errors &= ~UIDNA_ERROR_DOMAIN_NAME_TOO_LONG;
+  }
+
+  if (U_FAILURE(status) || (mode != IDNA_LENIENT && info.errors != 0)) {
     len = -1;
     buf->SetLength(0);
   } else {
@@ -564,9 +579,10 @@ static void ToASCII(const FunctionCallbackInfo<Value>& args) {
   Utf8Value val(env->isolate(), args[0]);
   // optional arg
   bool lenient = args[1]->BooleanValue(env->context()).FromJust();
+  enum idna_mode mode = lenient ? IDNA_LENIENT : IDNA_DEFAULT;
 
   MaybeStackBuffer<char> buf;
-  int32_t len = ToASCII(&buf, *val, val.length(), lenient);
+  int32_t len = ToASCII(&buf, *val, val.length(), mode);
 
   if (len < 0) {
     return env->ThrowError("Cannot convert name to ASCII");
diff --git a/src/node_i18n.h b/src/node_i18n.h
index cc1f3e6ea53569..adf9feb414df5c 100644
--- a/src/node_i18n.h
+++ b/src/node_i18n.h
@@ -37,10 +37,26 @@ namespace i18n {
 
 bool InitializeICUDirectory(const std::string& path);
 
+enum idna_mode {
+  // Default mode for maximum compatibility.
+  IDNA_DEFAULT,
+  // Ignore all errors in IDNA conversion, if possible.
+  IDNA_LENIENT,
+  // Enforce STD3 rules (UseSTD3ASCIIRules) and DNS length restrictions
+  // (VerifyDnsLength). Corresponds to `beStrict` flag in the "domain to ASCII"
+  // algorithm.
+  IDNA_STRICT
+};
+
+// Implements the WHATWG URL Standard "domain to ASCII" algorithm.
+// https://url.spec.whatwg.org/#concept-domain-to-ascii
 int32_t ToASCII(MaybeStackBuffer<char>* buf,
                 const char* input,
                 size_t length,
-                bool lenient = false);
+                enum idna_mode mode = IDNA_DEFAULT);
+
+// Implements the WHATWG URL Standard "domain to Unicode" algorithm.
+// https://url.spec.whatwg.org/#concept-domain-to-unicode
 int32_t ToUnicode(MaybeStackBuffer<char>* buf,
                   const char* input,
                   size_t length);
diff --git a/test/fixtures/url-idna.js b/test/fixtures/url-idna.js
index cbfe702e9372bf..4b8f5a48cc9646 100644
--- a/test/fixtures/url-idna.js
+++ b/test/fixtures/url-idna.js
@@ -1,223 +1,215 @@
 'use strict';
 
 // Credit for list: http://www.i18nguy.com/markup/idna-examples.html
-module.exports = {
-  valid: [
-    { ascii: 'xn--mgbaal8b0b9b2b.icom.museum',
-      unicode: 'افغانستا.icom.museum'
-    },
-    {
-      ascii: 'xn--lgbbat1ad8j.icom.museum',
-      unicode: 'الجزائر.icom.museum'
-    },
-    {
-      ascii: 'xn--sterreich-z7a.icom.museum',
-      unicode: 'österreich.icom.museum'
-    },
-    {
-      ascii: 'xn--54b6eqazv8bc7e.icom.museum',
-      unicode: 'বাংলাদেশ.icom.museum'
-    },
-    {
-      ascii: 'xn--80abmy0agn7e.icom.museum',
-      unicode: 'беларусь.icom.museum'
-    },
-    {
-      ascii: 'xn--belgi-rsa.icom.museum',
-      unicode: 'belgië.icom.museum'
-    },
-    {
-      ascii: 'xn--80abgvm6a7d2b.icom.museum',
-      unicode: 'българия.icom.museum'
-    },
-    {
-      ascii: 'xn--mgbfqim.icom.museum',
-      unicode: 'تشادر.icom.museum'
-    },
-    {
-      ascii: 'xn--fiqs8s.icom.museum',
-      unicode: '中国.icom.museum'
-    },
-    {
-      ascii: 'xn--mgbu4chg.icom.museum',
-      unicode: 'القمر.icom.museum'
-    },
-    {
-      ascii: 'xn--vxakcego.icom.museum',
-      unicode: 'κυπρος.icom.museum'
-    },
-    {
-      ascii: 'xn--eskrepublika-ebb62d.icom.museum',
-      unicode: 'českárepublika.icom.museum'
-    },
-    {
-      ascii: 'xn--wgbh1c.icom.museum',
-      unicode: 'مصر.icom.museum'
-    },
-    {
-      ascii: 'xn--hxakic4aa.icom.museum',
-      unicode: 'ελλάδα.icom.museum'
-    },
-    {
-      ascii: 'xn--magyarorszg-t7a.icom.museum',
-      unicode: 'magyarország.icom.museum'
-    },
-    {
-      ascii: 'xn--sland-ysa.icom.museum',
-      unicode: 'ísland.icom.museum'
-    },
-    {
-      ascii: 'xn--h2brj9c.icom.museum',
-      unicode: 'भारत.icom.museum'
-    },
-    {
-      ascii: 'xn--mgba3a4fra.icom.museum',
-      unicode: 'ايران.icom.museum'
-    },
-    {
-      ascii: 'xn--ire-9la.icom.museum',
-      unicode: 'éire.icom.museum'
-    },
-    {
-      ascii: 'xn--4dbklr2c8d.xn--4dbrk0ce.museum',
-      unicode: 'איקו״ם.ישראל.museum'
-    },
-    {
-      ascii: 'xn--wgv71a.icom.museum',
-      unicode: '日本.icom.museum'
-    },
-    {
-      ascii: 'xn--igbhzh7gpa.icom.museum',
-      unicode: 'الأردن.icom.museum'
-    },
-    {
-      ascii: 'xn--80aaa0a6awh12ed.icom.museum',
-      unicode: 'қазақстан.icom.museum'
-    },
-    {
-      ascii: 'xn--3e0b707e.icom.museum',
-      unicode: '한국.icom.museum'
-    },
-    {
-      ascii: 'xn--80afmksoji0fc.icom.museum',
-      unicode: 'кыргызстан.icom.museum'
-    },
-    {
-      ascii: 'xn--q7ce6a.icom.museum',
-      unicode: 'ລາວ.icom.museum'
-    },
-    {
-      ascii: 'xn--mgbb7fjb.icom.museum',
-      unicode: 'لبنان.icom.museum'
-    },
-    {
-      ascii: 'xn--80aaldqjmmi6x.icom.museum',
-      unicode: 'македонија.icom.museum'
-    },
-    {
-      ascii: 'xn--mgbah1a3hjkrd.icom.museum',
-      unicode: 'موريتانيا.icom.museum'
-    },
-    {
-      ascii: 'xn--mxico-bsa.icom.museum',
-      unicode: 'méxico.icom.museum'
-    },
-    {
-      ascii: 'xn--c1aqabffc0aq.icom.museum',
-      unicode: 'монголулс.icom.museum'
-    },
-    {
-      ascii: 'xn--mgbc0a9azcg.icom.museum',
-      unicode: 'المغرب.icom.museum'
-    },
-    {
-      ascii: 'xn--l2bey1c2b.icom.museum',
-      unicode: 'नेपाल.icom.museum'
-    },
-    {
-      ascii: 'xn--mgb9awbf.icom.museum',
-      unicode: 'عمان.icom.museum'
-    },
-    {
-      ascii: 'xn--wgbl6a.icom.museum',
-      unicode: 'قطر.icom.museum'
-    },
-    {
-      ascii: 'xn--romnia-yta.icom.museum',
-      unicode: 'românia.icom.museum'
-    },
-    {
-      ascii: 'xn--h1alffa9f.xn--h1aegh.museum',
-      unicode: 'россия.иком.museum'
-    },
-    {
-      ascii: 'xn--80aaabm1ab4blmeec9e7n.xn--h1aegh.museum',
-      unicode: 'србијаицрнагора.иком.museum'
-    },
-    {
-      ascii: 'xn--xkc2al3hye2a.icom.museum',
-      unicode: 'இலங்கை.icom.museum'
-    },
-    {
-      ascii: 'xn--espaa-rta.icom.museum',
-      unicode: 'españa.icom.museum'
-    },
-    {
-      ascii: 'xn--o3cw4h.icom.museum',
-      unicode: 'ไทย.icom.museum'
-    },
-    {
-      ascii: 'xn--pgbs0dh.icom.museum',
-      unicode: 'تونس.icom.museum'
-    },
-    {
-      ascii: 'xn--trkiye-3ya.icom.museum',
-      unicode: 'türkiye.icom.museum'
-    },
-    {
-      ascii: 'xn--80aaxgrpt.icom.museum',
-      unicode: 'украина.icom.museum'
-    },
-    {
-      ascii: 'xn--vitnam-jk8b.icom.museum',
-      unicode: 'việtnam.icom.museum'
-    },
-    // long label
-    {
-      ascii: `${'a'.repeat(64)}.com`,
-      unicode: `${'a'.repeat(64)}.com`,
-    },
-    // long URL
-    {
-      ascii: `${`${'a'.repeat(64)}.`.repeat(4)}com`,
-      unicode: `${`${'a'.repeat(64)}.`.repeat(4)}com`
-    },
-    // URLs with hyphen
-    {
-      ascii: 'r4---sn-a5mlrn7s.gevideo.com',
-      unicode: 'r4---sn-a5mlrn7s.gevideo.com'
-    },
-    {
-      ascii: '-sn-a5mlrn7s.gevideo.com',
-      unicode: '-sn-a5mlrn7s.gevideo.com'
-    },
-    {
-      ascii: 'sn-a5mlrn7s-.gevideo.com',
-      unicode: 'sn-a5mlrn7s-.gevideo.com'
-    },
-    {
-      ascii: '-sn-a5mlrn7s-.gevideo.com',
-      unicode: '-sn-a5mlrn7s-.gevideo.com'
-    },
-    {
-      ascii: '-sn--a5mlrn7s-.gevideo.com',
-      unicode: '-sn--a5mlrn7s-.gevideo.com'
-    }
-  ],
-  invalid: [
-    // invalid character
-    '\ufffd.com',
-    // invalid bi-directional character
-    'تشادرlatin.icom.museum'
-  ]
-}
+module.exports = [
+  { ascii: 'xn--mgbaal8b0b9b2b.icom.museum',
+    unicode: 'افغانستا.icom.museum'
+  },
+  {
+    ascii: 'xn--lgbbat1ad8j.icom.museum',
+    unicode: 'الجزائر.icom.museum'
+  },
+  {
+    ascii: 'xn--sterreich-z7a.icom.museum',
+    unicode: 'österreich.icom.museum'
+  },
+  {
+    ascii: 'xn--54b6eqazv8bc7e.icom.museum',
+    unicode: 'বাংলাদেশ.icom.museum'
+  },
+  {
+    ascii: 'xn--80abmy0agn7e.icom.museum',
+    unicode: 'беларусь.icom.museum'
+  },
+  {
+    ascii: 'xn--belgi-rsa.icom.museum',
+    unicode: 'belgië.icom.museum'
+  },
+  {
+    ascii: 'xn--80abgvm6a7d2b.icom.museum',
+    unicode: 'българия.icom.museum'
+  },
+  {
+    ascii: 'xn--mgbfqim.icom.museum',
+    unicode: 'تشادر.icom.museum'
+  },
+  {
+    ascii: 'xn--fiqs8s.icom.museum',
+    unicode: '中国.icom.museum'
+  },
+  {
+    ascii: 'xn--mgbu4chg.icom.museum',
+    unicode: 'القمر.icom.museum'
+  },
+  {
+    ascii: 'xn--vxakcego.icom.museum',
+    unicode: 'κυπρος.icom.museum'
+  },
+  {
+    ascii: 'xn--eskrepublika-ebb62d.icom.museum',
+    unicode: 'českárepublika.icom.museum'
+  },
+  {
+    ascii: 'xn--wgbh1c.icom.museum',
+    unicode: 'مصر.icom.museum'
+  },
+  {
+    ascii: 'xn--hxakic4aa.icom.museum',
+    unicode: 'ελλάδα.icom.museum'
+  },
+  {
+    ascii: 'xn--magyarorszg-t7a.icom.museum',
+    unicode: 'magyarország.icom.museum'
+  },
+  {
+    ascii: 'xn--sland-ysa.icom.museum',
+    unicode: 'ísland.icom.museum'
+  },
+  {
+    ascii: 'xn--h2brj9c.icom.museum',
+    unicode: 'भारत.icom.museum'
+  },
+  {
+    ascii: 'xn--mgba3a4fra.icom.museum',
+    unicode: 'ايران.icom.museum'
+  },
+  {
+    ascii: 'xn--ire-9la.icom.museum',
+    unicode: 'éire.icom.museum'
+  },
+  {
+    ascii: 'xn--4dbklr2c8d.xn--4dbrk0ce.museum',
+    unicode: 'איקו״ם.ישראל.museum'
+  },
+  {
+    ascii: 'xn--wgv71a.icom.museum',
+    unicode: '日本.icom.museum'
+  },
+  {
+    ascii: 'xn--igbhzh7gpa.icom.museum',
+    unicode: 'الأردن.icom.museum'
+  },
+  {
+    ascii: 'xn--80aaa0a6awh12ed.icom.museum',
+    unicode: 'қазақстан.icom.museum'
+  },
+  {
+    ascii: 'xn--3e0b707e.icom.museum',
+    unicode: '한국.icom.museum'
+  },
+  {
+    ascii: 'xn--80afmksoji0fc.icom.museum',
+    unicode: 'кыргызстан.icom.museum'
+  },
+  {
+    ascii: 'xn--q7ce6a.icom.museum',
+    unicode: 'ລາວ.icom.museum'
+  },
+  {
+    ascii: 'xn--mgbb7fjb.icom.museum',
+    unicode: 'لبنان.icom.museum'
+  },
+  {
+    ascii: 'xn--80aaldqjmmi6x.icom.museum',
+    unicode: 'македонија.icom.museum'
+  },
+  {
+    ascii: 'xn--mgbah1a3hjkrd.icom.museum',
+    unicode: 'موريتانيا.icom.museum'
+  },
+  {
+    ascii: 'xn--mxico-bsa.icom.museum',
+    unicode: 'méxico.icom.museum'
+  },
+  {
+    ascii: 'xn--c1aqabffc0aq.icom.museum',
+    unicode: 'монголулс.icom.museum'
+  },
+  {
+    ascii: 'xn--mgbc0a9azcg.icom.museum',
+    unicode: 'المغرب.icom.museum'
+  },
+  {
+    ascii: 'xn--l2bey1c2b.icom.museum',
+    unicode: 'नेपाल.icom.museum'
+  },
+  {
+    ascii: 'xn--mgb9awbf.icom.museum',
+    unicode: 'عمان.icom.museum'
+  },
+  {
+    ascii: 'xn--wgbl6a.icom.museum',
+    unicode: 'قطر.icom.museum'
+  },
+  {
+    ascii: 'xn--romnia-yta.icom.museum',
+    unicode: 'românia.icom.museum'
+  },
+  {
+    ascii: 'xn--h1alffa9f.xn--h1aegh.museum',
+    unicode: 'россия.иком.museum'
+  },
+  {
+    ascii: 'xn--80aaabm1ab4blmeec9e7n.xn--h1aegh.museum',
+    unicode: 'србијаицрнагора.иком.museum'
+  },
+  {
+    ascii: 'xn--xkc2al3hye2a.icom.museum',
+    unicode: 'இலங்கை.icom.museum'
+  },
+  {
+    ascii: 'xn--espaa-rta.icom.museum',
+    unicode: 'españa.icom.museum'
+  },
+  {
+    ascii: 'xn--o3cw4h.icom.museum',
+    unicode: 'ไทย.icom.museum'
+  },
+  {
+    ascii: 'xn--pgbs0dh.icom.museum',
+    unicode: 'تونس.icom.museum'
+  },
+  {
+    ascii: 'xn--trkiye-3ya.icom.museum',
+    unicode: 'türkiye.icom.museum'
+  },
+  {
+    ascii: 'xn--80aaxgrpt.icom.museum',
+    unicode: 'украина.icom.museum'
+  },
+  {
+    ascii: 'xn--vitnam-jk8b.icom.museum',
+    unicode: 'việtnam.icom.museum'
+  },
+  // long label
+  {
+    ascii: `${'a'.repeat(64)}.com`,
+    unicode: `${'a'.repeat(64)}.com`,
+  },
+  // long URL
+  {
+    ascii: `${`${'a'.repeat(64)}.`.repeat(4)}com`,
+    unicode: `${`${'a'.repeat(64)}.`.repeat(4)}com`
+  },
+  // URLs with hyphen
+  {
+    ascii: 'r4---sn-a5mlrn7s.gevideo.com',
+    unicode: 'r4---sn-a5mlrn7s.gevideo.com'
+  },
+  {
+    ascii: '-sn-a5mlrn7s.gevideo.com',
+    unicode: '-sn-a5mlrn7s.gevideo.com'
+  },
+  {
+    ascii: 'sn-a5mlrn7s-.gevideo.com',
+    unicode: 'sn-a5mlrn7s-.gevideo.com'
+  },
+  {
+    ascii: '-sn-a5mlrn7s-.gevideo.com',
+    unicode: '-sn-a5mlrn7s-.gevideo.com'
+  },
+  {
+    ascii: '-sn--a5mlrn7s-.gevideo.com',
+    unicode: '-sn--a5mlrn7s-.gevideo.com'
+  }
+];
diff --git a/test/fixtures/url-toascii.js b/test/fixtures/url-toascii.js
new file mode 100644
index 00000000000000..ea5e0f22ba1b5f
--- /dev/null
+++ b/test/fixtures/url-toascii.js
@@ -0,0 +1,156 @@
+'use strict';
+
+/* WPT Refs:
+   https://github.com/w3c/web-platform-tests/blob/4839a0a804/url/toascii.json
+   License: http://www.w3.org/Consortium/Legal/2008/04-testsuite-copyright.html
+*/
+module.exports =
+[
+  "This resource is focused on highlighting issues with UTS #46 ToASCII",
+  {
+    "comment": "Label with hyphens in 3rd and 4th position",
+    "input": "aa--",
+    "output": "aa--"
+  },
+  {
+    "input": "a†--",
+    "output": "xn--a---kp0a"
+  },
+  {
+    "input": "ab--c",
+    "output": "ab--c"
+  },
+  {
+    "comment": "Label with leading hyphen",
+    "input": "-x",
+    "output": "-x"
+  },
+  {
+    "input": "-†",
+    "output": "xn----xhn"
+  },
+  {
+    "input": "-x.xn--nxa",
+    "output": "-x.xn--nxa"
+  },
+  {
+    "input": "-x.β",
+    "output": "-x.xn--nxa"
+  },
+  {
+    "comment": "Label with trailing hyphen",
+    "input": "x-.xn--nxa",
+    "output": "x-.xn--nxa"
+  },
+  {
+    "input": "x-.β",
+    "output": "x-.xn--nxa"
+  },
+  {
+    "comment": "Empty labels",
+    "input": "x..xn--nxa",
+    "output": "x..xn--nxa"
+  },
+  {
+    "input": "x..β",
+    "output": "x..xn--nxa"
+  },
+  {
+    "comment": "Invalid Punycode",
+    "input": "xn--a",
+    "output": null
+  },
+  {
+    "input": "xn--a.xn--nxa",
+    "output": null
+  },
+  {
+    "input": "xn--a.β",
+    "output": null
+  },
+  {
+    "comment": "Valid Punycode",
+    "input": "xn--nxa.xn--nxa",
+    "output": "xn--nxa.xn--nxa"
+  },
+  {
+    "comment": "Mixed",
+    "input": "xn--nxa.β",
+    "output": "xn--nxa.xn--nxa"
+  },
+  {
+    "input": "ab--c.xn--nxa",
+    "output": "ab--c.xn--nxa"
+  },
+  {
+    "input": "ab--c.β",
+    "output": "ab--c.xn--nxa"
+  },
+  {
+    "comment": "CheckJoiners is true",
+    "input": "\u200D.example",
+    "output": null
+  },
+  {
+    "input": "xn--1ug.example",
+    "output": null
+  },
+  {
+    "comment": "CheckBidi is true",
+    "input": "يa",
+    "output": null
+  },
+  {
+    "input": "xn--a-yoc",
+    "output": null
+  },
+  {
+    "comment": "processing_option is Nontransitional_Processing",
+    "input": "ශ්‍රී",
+    "output": "xn--10cl1a0b660p"
+  },
+  {
+    "input": "نامه‌ای",
+    "output": "xn--mgba3gch31f060k"
+  },
+  {
+    "comment": "U+FFFD",
+    "input": "\uFFFD.com",
+    "output": null
+  },
+  {
+    "comment": "U+FFFD character encoded in Punycode",
+    "input": "xn--zn7c.com",
+    "output": null
+  },
+  {
+    "comment": "Label longer than 63 code points",
+    "input": "x01234567890123456789012345678901234567890123456789012345678901x",
+    "output": "x01234567890123456789012345678901234567890123456789012345678901x"
+  },
+  {
+    "input": "x01234567890123456789012345678901234567890123456789012345678901†",
+    "output": "xn--x01234567890123456789012345678901234567890123456789012345678901-6963b"
+  },
+  {
+    "input": "x01234567890123456789012345678901234567890123456789012345678901x.xn--nxa",
+    "output": "x01234567890123456789012345678901234567890123456789012345678901x.xn--nxa"
+  },
+  {
+    "input": "x01234567890123456789012345678901234567890123456789012345678901x.β",
+    "output": "x01234567890123456789012345678901234567890123456789012345678901x.xn--nxa"
+  },
+  {
+    "comment": "Domain excluding TLD longer than 253 code points",
+    "input": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.x",
+    "output": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.x"
+  },
+  {
+    "input": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.xn--nxa",
+    "output": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.xn--nxa"
+  },
+  {
+    "input": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.β",
+    "output": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.xn--nxa"
+  }
+]
diff --git a/test/parallel/test-icu-punycode.js b/test/parallel/test-icu-punycode.js
index ba2014bdc85a2f..13db2dd7bacede 100644
--- a/test/parallel/test-icu-punycode.js
+++ b/test/parallel/test-icu-punycode.js
@@ -10,9 +10,10 @@ const icu = process.binding('icu');
 const assert = require('assert');
 
 const tests = require('../fixtures/url-idna.js');
+const wptToASCIITests = require('../fixtures/url-toascii.js');
 
 {
-  for (const [i, { ascii, unicode }] of tests.valid.entries()) {
+  for (const [i, { ascii, unicode }] of tests.entries()) {
     assert.strictEqual(ascii, icu.toASCII(unicode), `toASCII(${i + 1})`);
     assert.strictEqual(unicode, icu.toUnicode(ascii), `toUnicode(${i + 1})`);
     assert.strictEqual(ascii, icu.toASCII(icu.toUnicode(ascii)),
@@ -23,13 +24,24 @@ const tests = require('../fixtures/url-idna.js');
 }
 
 {
-  for (const [i, url] of tests.invalid.entries()) {
-    assert.throws(() => icu.toASCII(url),
-                  /^Error: Cannot convert name to ASCII$/,
-                  `ToASCII invalid case ${i + 1}`);
-    assert.doesNotThrow(() => icu.toASCII(url, true),
-                        `ToASCII invalid case ${i + 1} in lenient mode`);
-    assert.doesNotThrow(() => icu.toUnicode(url),
-                        `ToUnicode invalid case ${i + 1}`);
+  for (const [i, test] of wptToASCIITests.entries()) {
+    if (typeof test === 'string')
+      continue; // skip comments
+    const { comment, input, output } = test;
+    let caseComment = `case ${i + 1}`;
+    if (comment)
+      caseComment += ` (${comment})`;
+    if (output === null) {
+      assert.throws(() => icu.toASCII(input),
+                    /^Error: Cannot convert name to ASCII$/,
+                    `ToASCII ${caseComment}`);
+      assert.doesNotThrow(() => icu.toASCII(input, true),
+                          `ToASCII ${caseComment} in lenient mode`);
+    } else {
+      assert.strictEqual(icu.toASCII(input), output, `ToASCII ${caseComment}`);
+      assert.strictEqual(icu.toASCII(input, true), output,
+                         `ToASCII ${caseComment} in lenient mode`);
+    }
+    assert.doesNotThrow(() => icu.toUnicode(input), `ToUnicode ${caseComment}`);
   }
 }
diff --git a/test/parallel/test-whatwg-url-domainto.js b/test/parallel/test-whatwg-url-domainto.js
index 90d9ee4a8c4648..b399f24136e14b 100644
--- a/test/parallel/test-whatwg-url-domainto.js
+++ b/test/parallel/test-whatwg-url-domainto.js
@@ -11,6 +11,7 @@ const { domainToASCII, domainToUnicode } = require('url');
 
 // Tests below are not from WPT.
 const tests = require('../fixtures/url-idna.js');
+const wptToASCIITests = require('../fixtures/url-toascii.js');
 
 {
   const expectedError = common.expectsError(
@@ -22,7 +23,7 @@ const tests = require('../fixtures/url-idna.js');
 }
 
 {
-  for (const [i, { ascii, unicode }] of tests.valid.entries()) {
+  for (const [i, { ascii, unicode }] of tests.entries()) {
     assert.strictEqual(ascii, domainToASCII(unicode),
                        `domainToASCII(${i + 1})`);
     assert.strictEqual(unicode, domainToUnicode(ascii),
@@ -35,8 +36,20 @@ const tests = require('../fixtures/url-idna.js');
 }
 
 {
-  for (const [i, url] of tests.invalid.entries()) {
-    assert.strictEqual(domainToASCII(url), '', `Invalid case ${i + 1}`);
-    assert.strictEqual(domainToUnicode(url), '', `Invalid case ${i + 1}`);
+  for (const [i, test] of wptToASCIITests.entries()) {
+    if (typeof test === 'string')
+      continue; // skip comments
+    const { comment, input, output } = test;
+    let caseComment = `Case ${i + 1}`;
+    if (comment)
+      caseComment += ` (${comment})`;
+    if (output === null) {
+      assert.strictEqual(domainToASCII(input), '', caseComment);
+      assert.strictEqual(domainToUnicode(input), '', caseComment);
+    } else {
+      assert.strictEqual(domainToASCII(input), output, caseComment);
+      const roundtripped = domainToASCII(domainToUnicode(input));
+      assert.strictEqual(roundtripped, output, caseComment);
+    }
   }
 }
diff --git a/test/parallel/test-whatwg-url-toascii.js b/test/parallel/test-whatwg-url-toascii.js
new file mode 100644
index 00000000000000..bd986c96a47a84
--- /dev/null
+++ b/test/parallel/test-whatwg-url-toascii.js
@@ -0,0 +1,85 @@
+'use strict';
+const common = require('../common');
+const path = require('path');
+const { URL } = require('url');
+const { test, assert_equals, assert_throws } = require('../common/wpt');
+
+if (!common.hasIntl) {
+  // A handful of the tests fail when ICU is not included.
+  common.skip('missing Intl');
+  return;
+}
+
+const request = {
+  response: require(path.join(common.fixturesDir, 'url-toascii'))
+};
+
+/* eslint-disable */
+/* WPT Refs:
+   https://github.com/w3c/web-platform-tests/blob/4839a0a804/url/toascii.window.js
+   License: http://www.w3.org/Consortium/Legal/2008/04-testsuite-copyright.html
+*/
+// async_test(t => {
+//   const request = new XMLHttpRequest()
+//   request.open("GET", "toascii.json")
+//   request.send()
+//   request.responseType = "json"
+//   request.onload = t.step_func_done(() => {
+    runTests(request.response)
+//   })
+// }, "Loading data…")
+
+function makeURL(type, input) {
+  input = "https://" + input + "/x"
+  if(type === "url") {
+    return new URL(input)
+  } else {
+    const url = document.createElement(type)
+    url.href = input
+    return url
+  }
+}
+
+function runTests(tests) {
+  for(var i = 0, l = tests.length; i < l; i++) {
+    let hostTest = tests[i]
+    if (typeof hostTest === "string") {
+      continue // skip comments
+    }
+    const typeName = { "url": "URL", "a": "<a>", "area": "<area>" }
+    // ;["url", "a", "area"].forEach((type) => {
+    ;["url"].forEach((type) => {
+      test(() => {
+        if(hostTest.output !== null) {
+          const url = makeURL("url", hostTest.input)
+          assert_equals(url.host, hostTest.output)
+          assert_equals(url.hostname, hostTest.output)
+          assert_equals(url.pathname, "/x")
+          assert_equals(url.href, "https://" + hostTest.output + "/x")
+        } else {
+          if(type === "url") {
+            assert_throws(new TypeError, () => makeURL("url", hostTest.input))
+          } else {
+            const url = makeURL(type, hostTest.input)
+            assert_equals(url.host, "")
+            assert_equals(url.hostname, "")
+            assert_equals(url.pathname, "")
+            assert_equals(url.href, "https://" + hostTest.input + "/x")
+          }
+        }
+      }, hostTest.input + " (using " + typeName[type] + ")")
+      ;["host", "hostname"].forEach((val) => {
+        test(() => {
+          const url = makeURL(type, "x")
+          url[val] = hostTest.input
+          if(hostTest.output !== null) {
+            assert_equals(url[val], hostTest.output)
+          } else {
+            assert_equals(url[val], "x")
+          }
+        }, hostTest.input + " (using " + typeName[type] + "." + val + ")")
+      })
+    })
+  }
+}
+/* eslint-enable */