diff --git a/lib/url.js b/lib/url.js
index 214c8a93204e70..f084fd372afaf9 100644
--- a/lib/url.js
+++ b/lib/url.js
@@ -311,7 +311,10 @@ Url.prototype.parse = function(url, parseQueryString, slashesDenoteHost) {
       // It only converts parts of the domain name that
       // have non-ASCII characters, i.e. it doesn't matter if
       // you call it with a domain that already is ASCII-only.
-      this.hostname = toASCII(this.hostname);
+
+      // Use lenient mode (`true`) to try to support even non-compliant
+      // URLs.
+      this.hostname = toASCII(this.hostname, true);
     }
 
     var p = this.port ? ':' + this.port : '';
diff --git a/src/node_i18n.cc b/src/node_i18n.cc
index 8e32f1fe08177b..c013027981755f 100644
--- a/src/node_i18n.cc
+++ b/src/node_i18n.cc
@@ -77,12 +77,11 @@ bool InitializeICUDirectory(const std::string& path) {
   }
 }
 
-static int32_t ToUnicode(MaybeStackBuffer<char>* buf,
-                         const char* input,
-                         size_t length) {
+int32_t ToUnicode(MaybeStackBuffer<char>* buf,
+                  const char* input,
+                  size_t length) {
   UErrorCode status = U_ZERO_ERROR;
-  uint32_t options = UIDNA_DEFAULT;
-  options |= UIDNA_NONTRANSITIONAL_TO_UNICODE;
+  uint32_t options = UIDNA_NONTRANSITIONAL_TO_UNICODE;
   UIDNA* uidna = uidna_openUTS46(options, &status);
   if (U_FAILURE(status))
     return -1;
@@ -90,33 +89,52 @@ static int32_t ToUnicode(MaybeStackBuffer<char>* buf,
 
   int32_t len = uidna_nameToUnicodeUTF8(uidna,
                                         input, length,
-                                        **buf, buf->length(),
+                                        **buf, buf->capacity(),
                                         &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);
     len = uidna_nameToUnicodeUTF8(uidna,
                                   input, length,
-                                  **buf, buf->length(),
+                                  **buf, buf->capacity(),
                                   &info,
                                   &status);
   }
 
-  if (U_FAILURE(status))
+  // info.errors is ignored as UTS #46 ToUnicode always produces a Unicode
+  // string, regardless of whether an error occurred.
+
+  if (U_FAILURE(status)) {
     len = -1;
+    buf->SetLength(0);
+  } else {
+    buf->SetLength(len);
+  }
 
   uidna_close(uidna);
   return len;
 }
 
-static int32_t ToASCII(MaybeStackBuffer<char>* buf,
-                       const char* input,
-                       size_t length) {
+int32_t ToASCII(MaybeStackBuffer<char>* buf,
+                const char* input,
+                size_t length,
+                enum idna_mode mode) {
   UErrorCode status = U_ZERO_ERROR;
-  uint32_t options = UIDNA_DEFAULT;
-  options |= UIDNA_NONTRANSITIONAL_TO_ASCII;
+  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;
@@ -124,7 +142,7 @@ static int32_t ToASCII(MaybeStackBuffer<char>* buf,
 
   int32_t len = uidna_nameToASCII_UTF8(uidna,
                                        input, length,
-                                       **buf, buf->length(),
+                                       **buf, buf->capacity(),
                                        &info,
                                        &status);
 
@@ -133,13 +151,45 @@ static int32_t ToASCII(MaybeStackBuffer<char>* buf,
     buf->AllocateSufficientStorage(len);
     len = uidna_nameToASCII_UTF8(uidna,
                                  input, length,
-                                 **buf, buf->length(),
+                                 **buf, buf->capacity(),
                                  &info,
                                  &status);
   }
 
-  if (U_FAILURE(status))
+  // 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 accommodate 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
+  // - http://www.unicode.org/review/pri317/
+  // - http://www.unicode.org/reports/tr46/tr46-18.html
+  // - https://www.icann.org/news/announcement-2000-01-07-en
+  info.errors &= ~UIDNA_ERROR_HYPHEN_3_4;
+  info.errors &= ~UIDNA_ERROR_LEADING_HYPHEN;
+  info.errors &= ~UIDNA_ERROR_TRAILING_HYPHEN;
+
+  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 {
+    buf->SetLength(len);
+  }
 
   uidna_close(uidna);
   return len;
@@ -169,8 +219,12 @@ static void ToASCII(const FunctionCallbackInfo<Value>& args) {
   CHECK_GE(args.Length(), 1);
   CHECK(args[0]->IsString());
   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());
+  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 ff9e87cea7fe83..30acefd1a8a996 100644
--- a/src/node_i18n.h
+++ b/src/node_i18n.h
@@ -16,6 +16,30 @@ 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,
+                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);
+
 }  // namespace i18n
 }  // namespace node
 
diff --git a/test/fixtures/url-idna.js b/test/fixtures/url-idna.js
new file mode 100644
index 00000000000000..4b8f5a48cc9646
--- /dev/null
+++ b/test/fixtures/url-idna.js
@@ -0,0 +1,215 @@
+'use strict';
+
+// Credit for list: http://www.i18nguy.com/markup/idna-examples.html
+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..59b76330f867f2
--- /dev/null
+++ b/test/fixtures/url-toascii.js
@@ -0,0 +1,157 @@
+'use strict';
+
+/* The following tests are copied from WPT. Modifications to them should be
+   upstreamed first. 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 cf83ac66206806..7abcae461774c0 100644
--- a/test/parallel/test-icu-punycode.js
+++ b/test/parallel/test-icu-punycode.js
@@ -1,70 +1,46 @@
 'use strict';
-
 const common = require('../common');
-const icu = getPunycode();
+
+if (!common.hasIntl)
+  common.skip('missing Intl');
+
+const icu = process.binding('icu');
 const assert = require('assert');
 
-function getPunycode() {
-  try {
-    return process.binding('icu');
-  } catch (err) {
-    return undefined;
+const tests = require('../fixtures/url-idna.js');
+const wptToASCIITests = require('../fixtures/url-toascii.js');
+
+{
+  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)),
+                       `toASCII(toUnicode(${i + 1}))`);
+    assert.strictEqual(unicode, icu.toUnicode(icu.toASCII(unicode)),
+                       `toUnicode(toASCII(${i + 1}))`);
   }
 }
 
-if (!icu)
-  common.skip('icu punycode tests because ICU is not present.');
+{
+  const errMessage = /^Error: Cannot convert name to ASCII$/;
 
-// Credit for list: http://www.i18nguy.com/markup/idna-examples.html
-const tests = [
-  'افغانستا.icom.museum',
-  'الجزائر.icom.museum',
-  'österreich.icom.museum',
-  'বাংলাদেশ.icom.museum',
-  'беларусь.icom.museum',
-  'belgië.icom.museum',
-  'българия.icom.museum',
-  'تشادر.icom.museum',
-  '中国.icom.museum',
-  'القمر.icom.museum',
-  'κυπρος.icom.museum',
-  'českárepublika.icom.museum',
-  'مصر.icom.museum',
-  'ελλάδα.icom.museum',
-  'magyarország.icom.museum',
-  'ísland.icom.museum',
-  'भारत.icom.museum',
-  'ايران.icom.museum',
-  'éire.icom.museum',
-  'איקו״ם.ישראל.museum',
-  '日本.icom.museum',
-  'الأردن.icom.museum',
-  'қазақстан.icom.museum',
-  '한국.icom.museum',
-  'кыргызстан.icom.museum',
-  'ລາວ.icom.museum',
-  'لبنان.icom.museum',
-  'македонија.icom.museum',
-  'موريتانيا.icom.museum',
-  'méxico.icom.museum',
-  'монголулс.icom.museum',
-  'المغرب.icom.museum',
-  'नेपाल.icom.museum',
-  'عمان.icom.museum',
-  'قطر.icom.museum',
-  'românia.icom.museum',
-  'россия.иком.museum',
-  'србијаицрнагора.иком.museum',
-  'இலங்கை.icom.museum',
-  'españa.icom.museum',
-  'ไทย.icom.museum',
-  'تونس.icom.museum',
-  'türkiye.icom.museum',
-  'украина.icom.museum',
-  'việtnam.icom.museum'
-];
-
-// Testing the roundtrip
-tests.forEach((i) => {
-  assert.strictEqual(i, icu.toUnicode(icu.toASCII(i)));
-});
+  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),
+                    errMessage, `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}`);
+  }
+}