diff --git a/lib/internal/url.js b/lib/internal/url.js
index 76530f2edc1998..6e6cc62226766b 100644
--- a/lib/internal/url.js
+++ b/lib/internal/url.js
@@ -23,6 +23,18 @@ const IteratorPrototype = Object.getPrototypeOf(
   Object.getPrototypeOf([][Symbol.iterator]())
 );
 
+const unpairedSurrogateRe =
+    /([^\uD800-\uDBFF]|^)[\uDC00-\uDFFF]|[\uD800-\uDBFF](?![\uDC00-\uDFFF])/;
+function toUSVString(val) {
+  const str = '' + val;
+  // As of V8 5.5, `str.search()` (and `unpairedSurrogateRe[@@search]()`) are
+  // slower than `unpairedSurrogateRe.exec()`.
+  const match = unpairedSurrogateRe.exec(str);
+  if (!match)
+    return str;
+  return binding.toUSVString(str, match.index);
+}
+
 class OpaqueOrigin {
   toString() {
     return 'null';
@@ -104,7 +116,6 @@ function onParseComplete(flags, protocol, username, password,
 
 // Reused by URL constructor and URL#href setter.
 function parse(url, input, base) {
-  input = String(input);
   const base_context = base ? base[context] : undefined;
   url[context] = new StorageObject();
   binding.parse(input.trim(), -1,
@@ -206,8 +217,10 @@ function onParseHashComplete(flags, protocol, username, password,
 
 class URL {
   constructor(input, base) {
+    // toUSVString is not needed.
+    input = '' + input;
     if (base !== undefined && !(base instanceof URL))
-      base = new URL(String(base));
+      base = new URL(base);
     parse(this, input, base);
   }
 
@@ -315,6 +328,8 @@ Object.defineProperties(URL.prototype, {
       return this[kFormat]({});
     },
     set(input) {
+      // toUSVString is not needed.
+      input = '' + input;
       parse(this, input);
     }
   },
@@ -332,7 +347,8 @@ Object.defineProperties(URL.prototype, {
       return this[context].scheme;
     },
     set(scheme) {
-      scheme = String(scheme);
+      // toUSVString is not needed.
+      scheme = '' + scheme;
       if (scheme.length === 0)
         return;
       binding.parse(scheme, binding.kSchemeStart, null, this[context],
@@ -346,7 +362,8 @@ Object.defineProperties(URL.prototype, {
       return this[context].username || '';
     },
     set(username) {
-      username = String(username);
+      // toUSVString is not needed.
+      username = '' + username;
       if (!this.hostname)
         return;
       const ctx = this[context];
@@ -366,7 +383,8 @@ Object.defineProperties(URL.prototype, {
       return this[context].password || '';
     },
     set(password) {
-      password = String(password);
+      // toUSVString is not needed.
+      password = '' + password;
       if (!this.hostname)
         return;
       const ctx = this[context];
@@ -391,7 +409,8 @@ Object.defineProperties(URL.prototype, {
     },
     set(host) {
       const ctx = this[context];
-      host = String(host);
+      // toUSVString is not needed.
+      host = '' + host;
       if (this[cannotBeBase] ||
           (this[special] && host.length === 0)) {
         // Cannot set the host if cannot-be-base is set or
@@ -415,7 +434,8 @@ Object.defineProperties(URL.prototype, {
     },
     set(host) {
       const ctx = this[context];
-      host = String(host);
+      // toUSVString is not needed.
+      host = '' + host;
       if (this[cannotBeBase] ||
           (this[special] && host.length === 0)) {
         // Cannot set the host if cannot-be-base is set or
@@ -439,11 +459,12 @@ Object.defineProperties(URL.prototype, {
       return port === undefined ? '' : String(port);
     },
     set(port) {
+      // toUSVString is not needed.
+      port = '' + port;
       const ctx = this[context];
       if (!ctx.host || this[cannotBeBase] ||
           this.protocol === 'file:')
         return;
-      port = String(port);
       if (port === '') {
         ctx.port = undefined;
         return;
@@ -462,9 +483,11 @@ Object.defineProperties(URL.prototype, {
       return ctx.path !== undefined ? `/${ctx.path.join('/')}` : '';
     },
     set(path) {
+      // toUSVString is not needed.
+      path = '' + path;
       if (this[cannotBeBase])
         return;
-      binding.parse(String(path), binding.kPathStart, null, this[context],
+      binding.parse(path, binding.kPathStart, null, this[context],
                     onParsePathComplete.bind(this));
     }
   },
@@ -477,7 +500,7 @@ Object.defineProperties(URL.prototype, {
     },
     set(search) {
       const ctx = this[context];
-      search = String(search);
+      search = toUSVString(search);
       if (!search) {
         ctx.query = null;
         ctx.flags &= ~binding.URL_FLAGS_HAS_QUERY;
@@ -509,7 +532,8 @@ Object.defineProperties(URL.prototype, {
     },
     set(hash) {
       const ctx = this[context];
-      hash = String(hash);
+      // toUSVString is not needed.
+      hash = '' + hash;
       if (this.protocol === 'javascript:')
         return;
       if (!hash) {
@@ -652,19 +676,22 @@ class URLSearchParams {
           if (pair.length !== 2) {
             throw new TypeError('Each query pair must be a name/value tuple');
           }
-          this[searchParams].push(String(pair[0]), String(pair[1]));
+          const key = toUSVString(pair[0]);
+          const value = toUSVString(pair[1]);
+          this[searchParams].push(key, value);
         }
       } else {
         // record<USVString, USVString>
         this[searchParams] = [];
-        for (const key of Object.keys(init)) {
-          const value = String(init[key]);
+        for (var key of Object.keys(init)) {
+          key = toUSVString(key);
+          const value = toUSVString(init[key]);
           this[searchParams].push(key, value);
         }
       }
     } else {
       // USVString
-      init = String(init);
+      init = toUSVString(init);
       if (init[0] === '?') init = init.slice(1);
       initSearchParams(this, init);
     }
@@ -743,8 +770,8 @@ defineIDLClass(URLSearchParams.prototype, 'URLSearchParams', {
       throw new TypeError('"name" and "value" arguments must be specified');
     }
 
-    name = String(name);
-    value = String(value);
+    name = toUSVString(name);
+    value = toUSVString(value);
     this[searchParams].push(name, value);
     update(this[context], this);
   },
@@ -758,7 +785,7 @@ defineIDLClass(URLSearchParams.prototype, 'URLSearchParams', {
     }
 
     const list = this[searchParams];
-    name = String(name);
+    name = toUSVString(name);
     for (var i = 0; i < list.length;) {
       const cur = list[i];
       if (cur === name) {
@@ -779,7 +806,7 @@ defineIDLClass(URLSearchParams.prototype, 'URLSearchParams', {
     }
 
     const list = this[searchParams];
-    name = String(name);
+    name = toUSVString(name);
     for (var i = 0; i < list.length; i += 2) {
       if (list[i] === name) {
         return list[i + 1];
@@ -798,7 +825,7 @@ defineIDLClass(URLSearchParams.prototype, 'URLSearchParams', {
 
     const list = this[searchParams];
     const values = [];
-    name = String(name);
+    name = toUSVString(name);
     for (var i = 0; i < list.length; i += 2) {
       if (list[i] === name) {
         values.push(list[i + 1]);
@@ -816,7 +843,7 @@ defineIDLClass(URLSearchParams.prototype, 'URLSearchParams', {
     }
 
     const list = this[searchParams];
-    name = String(name);
+    name = toUSVString(name);
     for (var i = 0; i < list.length; i += 2) {
       if (list[i] === name) {
         return true;
@@ -834,8 +861,8 @@ defineIDLClass(URLSearchParams.prototype, 'URLSearchParams', {
     }
 
     const list = this[searchParams];
-    name = String(name);
-    value = String(value);
+    name = toUSVString(name);
+    value = toUSVString(value);
 
     // If there are any name-value pairs whose name is `name`, in `list`, set
     // the value of the first such name-value pair to `value` and remove the
@@ -1098,11 +1125,13 @@ function originFor(url, base) {
 }
 
 function domainToASCII(domain) {
-  return binding.domainToASCII(String(domain));
+  // toUSVString is not needed.
+  return binding.domainToASCII('' + domain);
 }
 
 function domainToUnicode(domain) {
-  return binding.domainToUnicode(String(domain));
+  // toUSVString is not needed.
+  return binding.domainToUnicode('' + domain);
 }
 
 // Utility function that converts a URL object into an ordinary
@@ -1188,11 +1217,14 @@ function getPathFromURL(path) {
   return isWindows ? getPathFromURLWin32(path) : getPathFromURLPosix(path);
 }
 
-exports.getPathFromURL = getPathFromURL;
-exports.URL = URL;
-exports.URLSearchParams = URLSearchParams;
-exports.domainToASCII = domainToASCII;
-exports.domainToUnicode = domainToUnicode;
-exports.urlToOptions = urlToOptions;
-exports.formatSymbol = kFormat;
-exports.searchParamsSymbol = searchParams;
+module.exports = {
+  toUSVString,
+  getPathFromURL,
+  URL,
+  URLSearchParams,
+  domainToASCII,
+  domainToUnicode,
+  urlToOptions,
+  formatSymbol: kFormat,
+  searchParamsSymbol: searchParams
+};
diff --git a/src/node_url.cc b/src/node_url.cc
index 5027399e89dd71..b2f1322ade3cc0 100644
--- a/src/node_url.cc
+++ b/src/node_url.cc
@@ -20,6 +20,8 @@
 #include <unicode/utf.h>
 #endif
 
+#define UNICODE_REPLACEMENT_CHARACTER 0xFFFD
+
 namespace node {
 
 using v8::Array;
@@ -143,6 +145,21 @@ namespace url {
   }
 #endif
 
+  // If a UTF-16 character is a low/trailing surrogate.
+  static inline bool IsUnicodeTrail(uint16_t c) {
+    return (c & 0xFC00) == 0xDC00;
+  }
+
+  // If a UTF-16 character is a surrogate.
+  static inline bool IsUnicodeSurrogate(uint16_t c) {
+    return (c & 0xF800) == 0xD800;
+  }
+
+  // If a UTF-16 surrogate is a low/trailing one.
+  static inline bool IsUnicodeSurrogateTrail(uint16_t c) {
+    return (c & 0x400) != 0;
+  }
+
   static url_host_type ParseIPv6Host(url_host* host,
                                      const char* input,
                                      size_t length) {
@@ -1351,6 +1368,41 @@ namespace url {
                             v8::NewStringType::kNormal).ToLocalChecked());
   }
 
+  static void ToUSVString(const FunctionCallbackInfo<Value>& args) {
+    Environment* env = Environment::GetCurrent(args);
+    CHECK_GE(args.Length(), 2);
+    CHECK(args[0]->IsString());
+    CHECK(args[1]->IsNumber());
+
+    TwoByteValue value(env->isolate(), args[0]);
+    const size_t n = value.length();
+
+    const int64_t start = args[1]->IntegerValue(env->context()).FromJust();
+    CHECK_GE(start, 0);
+
+    for (size_t i = start; i < n; i++) {
+      uint16_t c = value[i];
+      if (!IsUnicodeSurrogate(c)) {
+        continue;
+      } else if (IsUnicodeSurrogateTrail(c) || i == n - 1) {
+        value[i] = UNICODE_REPLACEMENT_CHARACTER;
+      } else {
+        uint16_t d = value[i + 1];
+        if (IsUnicodeTrail(d)) {
+          i++;
+        } else {
+          value[i] = UNICODE_REPLACEMENT_CHARACTER;
+        }
+      }
+    }
+
+    args.GetReturnValue().Set(
+        String::NewFromTwoByte(env->isolate(),
+                               *value,
+                               v8::NewStringType::kNormal,
+                               n).ToLocalChecked());
+  }
+
   static void DomainToASCII(const FunctionCallbackInfo<Value>& args) {
     Environment* env = Environment::GetCurrent(args);
     CHECK_GE(args.Length(), 1);
@@ -1398,6 +1450,7 @@ namespace url {
     Environment* env = Environment::GetCurrent(context);
     env->SetMethod(target, "parse", Parse);
     env->SetMethod(target, "encodeAuth", EncodeAuthSet);
+    env->SetMethod(target, "toUSVString", ToUSVString);
     env->SetMethod(target, "domainToASCII", DomainToASCII);
     env->SetMethod(target, "domainToUnicode", DomainToUnicode);
 
diff --git a/test/fixtures/url-setter-tests-additional.js b/test/fixtures/url-setter-tests-additional.js
new file mode 100644
index 00000000000000..b27ae336a28776
--- /dev/null
+++ b/test/fixtures/url-setter-tests-additional.js
@@ -0,0 +1,237 @@
+module.exports = {
+  'username': [
+    {
+      'comment': 'Surrogate pair',
+      'href': 'https://github.com/',
+      'new_value': '\uD83D\uDE00',
+      'expected': {
+        'href': 'https://%F0%9F%98%80@github.com/',
+        'username': '%F0%9F%98%80'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '\uD83D',
+      'expected': {
+        'href': 'https://%EF%BF%BD@github.com/',
+        'username': '%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '\uD83Dnode',
+      'expected': {
+        'href': 'https://%EF%BF%BDnode@github.com/',
+        'username': '%EF%BF%BDnode'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '\uDE00',
+      'expected': {
+        'href': 'https://%EF%BF%BD@github.com/',
+        'username': '%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '\uDE00node',
+      'expected': {
+        'href': 'https://%EF%BF%BDnode@github.com/',
+        'username': '%EF%BF%BDnode'
+      }
+    }
+  ],
+  'password': [
+    {
+      'comment': 'Surrogate pair',
+      'href': 'https://github.com/',
+      'new_value': '\uD83D\uDE00',
+      'expected': {
+        'href': 'https://:%F0%9F%98%80@github.com/',
+        'password': '%F0%9F%98%80'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '\uD83D',
+      'expected': {
+        'href': 'https://:%EF%BF%BD@github.com/',
+        'password': '%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '\uD83Dnode',
+      'expected': {
+        'href': 'https://:%EF%BF%BDnode@github.com/',
+        'password': '%EF%BF%BDnode'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '\uDE00',
+      'expected': {
+        'href': 'https://:%EF%BF%BD@github.com/',
+        'password': '%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '\uDE00node',
+      'expected': {
+        'href': 'https://:%EF%BF%BDnode@github.com/',
+        'password': '%EF%BF%BDnode'
+      }
+    }
+  ],
+  'pathname': [
+    {
+      'comment': 'Surrogate pair',
+      'href': 'https://github.com/',
+      'new_value': '/\uD83D\uDE00',
+      'expected': {
+        'href': 'https://github.com/%F0%9F%98%80',
+        'pathname': '/%F0%9F%98%80'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '/\uD83D',
+      'expected': {
+        'href': 'https://github.com/%EF%BF%BD',
+        'pathname': '/%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '/\uD83Dnode',
+      'expected': {
+        'href': 'https://github.com/%EF%BF%BDnode',
+        'pathname': '/%EF%BF%BDnode'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '/\uDE00',
+      'expected': {
+        'href': 'https://github.com/%EF%BF%BD',
+        'pathname': '/%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '/\uDE00node',
+      'expected': {
+        'href': 'https://github.com/%EF%BF%BDnode',
+        'pathname': '/%EF%BF%BDnode'
+      }
+    }
+  ],
+  'search': [
+    {
+      'comment': 'Surrogate pair',
+      'href': 'https://github.com/',
+      'new_value': '\uD83D\uDE00',
+      'expected': {
+        'href': 'https://github.com/?%F0%9F%98%80',
+        'search': '?%F0%9F%98%80'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '\uD83D',
+      'expected': {
+        'href': 'https://github.com/?%EF%BF%BD',
+        'search': '?%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '\uD83Dnode',
+      'expected': {
+        'href': 'https://github.com/?%EF%BF%BDnode',
+        'search': '?%EF%BF%BDnode'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '\uDE00',
+      'expected': {
+        'href': 'https://github.com/?%EF%BF%BD',
+        'search': '?%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '\uDE00node',
+      'expected': {
+        'href': 'https://github.com/?%EF%BF%BDnode',
+        'search': '?%EF%BF%BDnode'
+      }
+    }
+  ],
+  'hash': [
+    {
+      'comment': 'Surrogate pair',
+      'href': 'https://github.com/',
+      'new_value': '\uD83D\uDE00',
+      'expected': {
+        'href': 'https://github.com/#%F0%9F%98%80',
+        'hash': '#%F0%9F%98%80'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '\uD83D',
+      'expected': {
+        'href': 'https://github.com/#%EF%BF%BD',
+        'hash': '#%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired low surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '\uD83Dnode',
+      'expected': {
+        'href': 'https://github.com/#%EF%BF%BDnode',
+        'hash': '#%EF%BF%BDnode'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 1',
+      'href': 'https://github.com/',
+      'new_value': '\uDE00',
+      'expected': {
+        'href': 'https://github.com/#%EF%BF%BD',
+        'hash': '#%EF%BF%BD'
+      }
+    },
+    {
+      'comment': 'Unpaired high surrogate 2',
+      'href': 'https://github.com/',
+      'new_value': '\uDE00node',
+      'expected': {
+        'href': 'https://github.com/#%EF%BF%BDnode',
+        'hash': '#%EF%BF%BDnode'
+      }
+    }
+  ]
+};
diff --git a/test/fixtures/url-tests-additional.js b/test/fixtures/url-tests-additional.js
index ffe47fb639dcba..c1c640f4bb4b7d 100644
--- a/test/fixtures/url-tests-additional.js
+++ b/test/fixtures/url-tests-additional.js
@@ -3,4 +3,34 @@
 // This file contains test cases not part of the WPT
 
 module.exports = [
+  {
+    // surrogate pair
+    'url': 'https://github.com/nodejs/\uD83D\uDE00node',
+    'protocol': 'https:',
+    'pathname': '/nodejs/%F0%9F%98%80node'
+  },
+  {
+    // unpaired low surrogate
+    'url': 'https://github.com/nodejs/\uD83D',
+    'protocol': 'https:',
+    'pathname': '/nodejs/%EF%BF%BD'
+  },
+  {
+    // unpaired low surrogate
+    'url': 'https://github.com/nodejs/\uD83Dnode',
+    'protocol': 'https:',
+    'pathname': '/nodejs/%EF%BF%BDnode'
+  },
+  {
+    // unmatched high surrogate
+    'url': 'https://github.com/nodejs/\uDE00',
+    'protocol': 'https:',
+    'pathname': '/nodejs/%EF%BF%BD'
+  },
+  {
+    // unmatched high surrogate
+    'url': 'https://github.com/nodejs/\uDE00node',
+    'protocol': 'https:',
+    'pathname': '/nodejs/%EF%BF%BDnode'
+  }
 ];
diff --git a/test/parallel/test-whatwg-url-searchparams-append.js b/test/parallel/test-whatwg-url-searchparams-append.js
index 2e3a33b26307c3..67eddbcc503e1e 100644
--- a/test/parallel/test-whatwg-url-searchparams-append.js
+++ b/test/parallel/test-whatwg-url-searchparams-append.js
@@ -57,4 +57,13 @@ test(function() {
   assert.throws(() => {
     params.set('a');
   }, /^TypeError: "name" and "value" arguments must be specified$/);
+
+  const obj = { toString() { throw new Error('toString'); } };
+  const sym = Symbol();
+  assert.throws(() => params.set(obj, 'b'), /^Error: toString$/);
+  assert.throws(() => params.set('a', obj), /^Error: toString$/);
+  assert.throws(() => params.set(sym, 'b'),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
+  assert.throws(() => params.set('a', sym),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
 }
diff --git a/test/parallel/test-whatwg-url-searchparams-constructor.js b/test/parallel/test-whatwg-url-searchparams-constructor.js
index d57373e727ac51..8ccd8f9427f160 100644
--- a/test/parallel/test-whatwg-url-searchparams-constructor.js
+++ b/test/parallel/test-whatwg-url-searchparams-constructor.js
@@ -207,3 +207,19 @@ test(() => {
   assert.throws(() => new URLSearchParams([{ [Symbol.iterator]: 42 }]),
                 /^TypeError: Each query pair must be iterable$/);
 }
+
+{
+  const obj = { toString() { throw new Error('toString'); } };
+  const sym = Symbol();
+
+  assert.throws(() => new URLSearchParams({ a: obj }), /^Error: toString$/);
+  assert.throws(() => new URLSearchParams([['a', obj]]), /^Error: toString$/);
+  assert.throws(() => new URLSearchParams(sym),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
+  assert.throws(() => new URLSearchParams({ a: sym }),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
+  assert.throws(() => new URLSearchParams([[sym, 'a']]),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
+  assert.throws(() => new URLSearchParams([['a', sym]]),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
+}
diff --git a/test/parallel/test-whatwg-url-searchparams-delete.js b/test/parallel/test-whatwg-url-searchparams-delete.js
index c6235263f22bad..d0bae75b4718a8 100644
--- a/test/parallel/test-whatwg-url-searchparams-delete.js
+++ b/test/parallel/test-whatwg-url-searchparams-delete.js
@@ -51,6 +51,12 @@ test(function() {
   assert.throws(() => {
     params.delete();
   }, /^TypeError: "name" argument must be specified$/);
+
+  const obj = { toString() { throw new Error('toString'); } };
+  const sym = Symbol();
+  assert.throws(() => params.delete(obj), /^Error: toString$/);
+  assert.throws(() => params.delete(sym),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
 }
 
 // https://github.com/nodejs/node/issues/10480
diff --git a/test/parallel/test-whatwg-url-searchparams-get.js b/test/parallel/test-whatwg-url-searchparams-get.js
index 3a46993214a997..2244fc28612755 100644
--- a/test/parallel/test-whatwg-url-searchparams-get.js
+++ b/test/parallel/test-whatwg-url-searchparams-get.js
@@ -42,4 +42,10 @@ test(function() {
   assert.throws(() => {
     params.get();
   }, /^TypeError: "name" argument must be specified$/);
+
+  const obj = { toString() { throw new Error('toString'); } };
+  const sym = Symbol();
+  assert.throws(() => params.get(obj), /^Error: toString$/);
+  assert.throws(() => params.get(sym),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
 }
diff --git a/test/parallel/test-whatwg-url-searchparams-getall.js b/test/parallel/test-whatwg-url-searchparams-getall.js
index df055e009e7e4d..921a6c9bc66da2 100644
--- a/test/parallel/test-whatwg-url-searchparams-getall.js
+++ b/test/parallel/test-whatwg-url-searchparams-getall.js
@@ -46,4 +46,10 @@ test(function() {
   assert.throws(() => {
     params.getAll();
   }, /^TypeError: "name" argument must be specified$/);
+
+  const obj = { toString() { throw new Error('toString'); } };
+  const sym = Symbol();
+  assert.throws(() => params.getAll(obj), /^Error: toString$/);
+  assert.throws(() => params.getAll(sym),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
 }
diff --git a/test/parallel/test-whatwg-url-searchparams-has.js b/test/parallel/test-whatwg-url-searchparams-has.js
index 1be9cf6121593e..9d7272f999c653 100644
--- a/test/parallel/test-whatwg-url-searchparams-has.js
+++ b/test/parallel/test-whatwg-url-searchparams-has.js
@@ -45,4 +45,10 @@ test(function() {
   assert.throws(() => {
     params.has();
   }, /^TypeError: "name" argument must be specified$/);
+
+  const obj = { toString() { throw new Error('toString'); } };
+  const sym = Symbol();
+  assert.throws(() => params.has(obj), /^Error: toString$/);
+  assert.throws(() => params.has(sym),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
 }
diff --git a/test/parallel/test-whatwg-url-searchparams-set.js b/test/parallel/test-whatwg-url-searchparams-set.js
index e78ce4763158b5..0eee7b5c9a0130 100644
--- a/test/parallel/test-whatwg-url-searchparams-set.js
+++ b/test/parallel/test-whatwg-url-searchparams-set.js
@@ -43,4 +43,13 @@ test(function() {
   assert.throws(() => {
     params.set('a');
   }, /^TypeError: "name" and "value" arguments must be specified$/);
+
+  const obj = { toString() { throw new Error('toString'); } };
+  const sym = Symbol();
+  assert.throws(() => params.append(obj, 'b'), /^Error: toString$/);
+  assert.throws(() => params.append('a', obj), /^Error: toString$/);
+  assert.throws(() => params.append(sym, 'b'),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
+  assert.throws(() => params.append('a', sym),
+                /^TypeError: Cannot convert a Symbol value to a string$/);
 }
diff --git a/test/parallel/test-whatwg-url-searchparams.js b/test/parallel/test-whatwg-url-searchparams.js
index 36fac3a2307ecc..e0d1826596704c 100644
--- a/test/parallel/test-whatwg-url-searchparams.js
+++ b/test/parallel/test-whatwg-url-searchparams.js
@@ -5,8 +5,14 @@ const assert = require('assert');
 const URL = require('url').URL;
 
 // Tests below are not from WPT.
-const serialized = 'a=a&a=1&a=true&a=undefined&a=null&a=%5Bobject%20Object%5D';
-const values = ['a', 1, true, undefined, null, {}];
+const serialized = 'a=a&a=1&a=true&a=undefined&a=null&a=%EF%BF%BD' +
+                   '&a=%EF%BF%BD&a=%F0%9F%98%80&a=%EF%BF%BD%EF%BF%BD' +
+                   '&a=%5Bobject%20Object%5D';
+const values = ['a', 1, true, undefined, null, '\uD83D', '\uDE00',
+                '\uD83D\uDE00', '\uDE00\uD83D', {}];
+const normalizedValues = ['a', '1', 'true', 'undefined', 'null', '\uFFFD',
+                          '\uFFFD', '\uD83D\uDE00', '\uFFFD\uFFFD',
+                          '[object Object]'];
 
 const m = new URL('http://example.org');
 const sp = m.searchParams;
@@ -27,7 +33,7 @@ assert.strictEqual(sp.toString(), '');
 
 values.forEach((i) => sp.append('a', i));
 assert(sp.has('a'));
-assert.strictEqual(sp.getAll('a').length, 6);
+assert.strictEqual(sp.getAll('a').length, values.length);
 assert.strictEqual(sp.get('a'), 'a');
 
 assert.strictEqual(sp.toString(), serialized);
@@ -39,23 +45,27 @@ assert.strictEqual(sp[Symbol.iterator], sp.entries);
 let key, val;
 let n = 0;
 for ([key, val] of sp) {
-  assert.strictEqual(key, 'a');
-  assert.strictEqual(val, String(values[n++]));
+  assert.strictEqual(key, 'a', n);
+  assert.strictEqual(val, normalizedValues[n], n);
+  n++;
 }
 n = 0;
 for (key of sp.keys()) {
-  assert.strictEqual(key, 'a');
+  assert.strictEqual(key, 'a', n);
+  n++;
 }
 n = 0;
 for (val of sp.values()) {
-  assert.strictEqual(val, String(values[n++]));
+  assert.strictEqual(val, normalizedValues[n], n);
+  n++;
 }
 n = 0;
 sp.forEach(function(val, key, obj) {
-  assert.strictEqual(this, undefined);
-  assert.strictEqual(key, 'a');
-  assert.strictEqual(val, String(values[n++]));
-  assert.strictEqual(obj, sp);
+  assert.strictEqual(this, undefined, n);
+  assert.strictEqual(key, 'a', n);
+  assert.strictEqual(val, normalizedValues[n], n);
+  assert.strictEqual(obj, sp, n);
+  n++;
 });
 sp.forEach(function() {
   assert.strictEqual(this, m);
diff --git a/test/parallel/test-whatwg-url-setters.js b/test/parallel/test-whatwg-url-setters.js
index 409ed1bd00d36c..6342243c78fd17 100644
--- a/test/parallel/test-whatwg-url-setters.js
+++ b/test/parallel/test-whatwg-url-setters.js
@@ -1,9 +1,12 @@
 'use strict';
 
 const common = require('../common');
+const assert = require('assert');
 const path = require('path');
 const URL = require('url').URL;
 const { test, assert_equals } = common.WPT;
+const additionalTestCases = require(
+    path.join(common.fixturesDir, 'url-setter-tests-additional.js'));
 
 if (!common.hasIntl) {
   // A handful of the tests fail when ICU is not included.
@@ -76,3 +79,45 @@ function runURLSettersTests(all_test_cases) {
 
 startURLSettersTests()
 /* eslint-enable */
+
+// Tests below are not from WPT.
+
+{
+  for (const attributeToBeSet in additionalTestCases) {
+    if (attributeToBeSet === 'comment') {
+      continue;
+    }
+    const testCases = additionalTestCases[attributeToBeSet];
+    for (const testCase of testCases) {
+      let name = `Setting <${testCase.href}>.${attributeToBeSet}` +
+                 ` = "${testCase.new_value}"`;
+      if ('comment' in testCase) {
+        name += ' ' + testCase.comment;
+      }
+      test(function() {
+        const url = new URL(testCase.href);
+        url[attributeToBeSet] = testCase.new_value;
+        for (const attribute in testCase.expected) {
+          assert_equals(url[attribute], testCase.expected[attribute]);
+        }
+      }, 'URL: ' + name);
+    }
+  }
+}
+
+{
+  const url = new URL('http://example.com/');
+  const obj = { toString() { throw new Error('toString'); } };
+  const sym = Symbol();
+  const props = Object.getOwnPropertyDescriptors(Object.getPrototypeOf(url));
+  for (const [name, { set }] of Object.entries(props)) {
+    if (set) {
+      assert.throws(() => url[name] = obj,
+                    /^Error: toString$/,
+                    `url.${name} = { toString() { throw ... } }`);
+      assert.throws(() => url[name] = sym,
+                    /^TypeError: Cannot convert a Symbol value to a string$/,
+                    `url.${name} = ${String(sym)}`);
+    }
+  }
+}