diff --git a/core/modules/link/src/Plugin/migrate/process/d6/FieldLink.php b/core/modules/link/src/Plugin/migrate/process/d6/FieldLink.php
index 9d06c66..aaede46 100644
--- a/core/modules/link/src/Plugin/migrate/process/d6/FieldLink.php
+++ b/core/modules/link/src/Plugin/migrate/process/d6/FieldLink.php
@@ -53,16 +53,102 @@ protected function canonicalizeUri($uri) {
       return $uri;
     }
 
-    // If the URL starts with 'www.' without scheme, add 'http://' prefix.
-    if (strpos($uri, 'www.') === 0) {
-      $uri = 'http://' . $uri;
-      return $uri;
-    }
-
     // Remove the <front> component of the URL.
     if (strpos($uri, '<front>') === 0) {
       $uri = substr($uri, strlen('<front>'));
     }
+    else {
+      // @TODO Complete letters.
+      $LINK_ICHARS_DOMAIN = (string) html_entity_decode(implode("", [
+        "&#x00E6;", // æ
+        "&#x00C6;", // Æ
+        "&#x00C0;", // À
+        "&#x00E0;", // à
+        "&#x00C1;", // Á
+        "&#x00E1;", // á
+        "&#x00C2;", // Â
+        "&#x00E2;", // â
+        "&#x00E5;", // å
+        "&#x00C5;", // Å
+        "&#x00E4;", // ä
+        "&#x00C4;", // Ä
+        "&#x00C7;", // Ç
+        "&#x00E7;", // ç
+        "&#x00D0;", // Ð
+        "&#x00F0;", // ð
+        "&#x00C8;", // È
+        "&#x00E8;", // è
+        "&#x00C9;", // É
+        "&#x00E9;", // é
+        "&#x00CA;", // Ê
+        "&#x00EA;", // ê
+        "&#x00CB;", // Ë
+        "&#x00EB;", // ë
+        "&#x00CE;", // Î
+        "&#x00EE;", // î
+        "&#x00CF;", // Ï
+        "&#x00EF;", // ï
+        "&#x00F8;", // ø
+        "&#x00D8;", // Ø
+        "&#x00F6;", // ö
+        "&#x00D6;", // Ö
+        "&#x00D4;", // Ô
+        "&#x00F4;", // ô
+        "&#x00D5;", // Õ
+        "&#x00F5;", // õ
+        "&#x0152;", // Œ
+        "&#x0153;", // œ
+        "&#x00FC;", // ü
+        "&#x00DC;", // Ü
+        "&#x00D9;", // Ù
+        "&#x00F9;", // ù
+        "&#x00DB;", // Û
+        "&#x00FB;", // û
+        "&#x0178;", // Ÿ
+        "&#x00FF;", // ÿ
+        "&#x00D1;", // Ñ
+        "&#x00F1;", // ñ
+        "&#x00FE;", // þ
+        "&#x00DE;", // Þ
+        "&#x00FD;", // ý
+        "&#x00DD;", // Ý
+        "&#x00BF;", // ¿
+      ]), ENT_QUOTES, 'UTF-8');
+
+      $LINK_ICHARS = $LINK_ICHARS_DOMAIN . (string) html_entity_decode(implode("", [
+          "&#x00DF;", // ß
+        ]), ENT_QUOTES, 'UTF-8');
+
+      // Pattern specific to internal links.
+      $internal_pattern = "/^(?:[a-z0-9" . $LINK_ICHARS . "_\-+\[\] ]+)";
+
+      $directories = "(?:\/[a-z0-9" . $LINK_ICHARS . "_\-\.~+%=&,$'#!():;*@\[\]]*)*";
+      // Yes, four backslashes == a single backslash.
+      $query = "(?:\/?\?([?a-z0-9" . $LINK_ICHARS . "+_|\-\.~\/\\\\%=&,$'():;*@\[\]{} ]*))";
+      $anchor = "(?:#[a-z0-9" . $LINK_ICHARS . "_\-\.~+%=&,$'():;*@\[\]\/\?]*)";
+
+      // The rest of the path for a standard URL.
+      $end = $directories . '?' . $query . '?' . $anchor . '?' . '$/i';
+
+      if (!preg_match($internal_pattern . $end, $uri)) {
+        $allowed_protocols = ['http', 'https', 'ftp', 'news', 'nntp', 'telnet', 'mailto', 'irc', 'ssh', 'sftp', 'webcal'];
+        $LINK_DOMAINS = 'aero|arpa|asia|biz|com|cat|coop|edu|gov|info|int|jobs|mil|museum|name|nato|net|org|pro|travel|mobi|local';
+
+        // Starting a parenthesis group with (?: means that it is grouped, but is not captured
+        $protocol = '((?:' . implode("|", $allowed_protocols) . '):\/\/)';
+        $authentication = "(?:(?:(?:[\w\.\-\+!$&'\(\)*\+,;=" . $LINK_ICHARS . "]|%[0-9a-f]{2})+(?::(?:[\w" . $LINK_ICHARS . "\.\-\+%!$&'\(\)*\+,;=]|%[0-9a-f]{2})*)?)?@)";
+        $domain = '(?:(?:[a-z0-9' . $LINK_ICHARS_DOMAIN . ']([a-z0-9' . $LINK_ICHARS_DOMAIN . '\-_\[\]])*)(\.(([a-z0-9' . $LINK_ICHARS_DOMAIN . '\-_\[\]])+\.)*(' . $LINK_DOMAINS . '|[a-z]{2}))?)';
+        $ipv4 = '(?:[0-9]{1,3}(\.[0-9]{1,3}){3})';
+        $ipv6 = '(?:[0-9a-fA-F]{1,4}(\:[0-9a-fA-F]{1,4}){7})';
+        $port = '(?::([0-9]{1,5}))';
+
+        // Pattern specific to external links.
+        $external_pattern = '/^' . $protocol . '?' . $authentication . '?(' . $domain . '|' . $ipv4 . '|' . $ipv6 . ' |localhost)' . $port . '?';
+        if (preg_match($external_pattern . $end, $uri)) {
+          return 'http://' . $uri;
+        }
+      }
+    }
 
     // Add the internal: scheme and ensure a leading slash.
     return 'internal:/' . ltrim($uri, '/');
diff --git a/core/modules/link/tests/src/Unit/Plugin/migrate/process/d6/FieldLinkTest.php b/core/modules/link/tests/src/Unit/Plugin/migrate/process/d6/FieldLinkTest.php
index c933fcd..5815390 100644
--- a/core/modules/link/tests/src/Unit/Plugin/migrate/process/d6/FieldLinkTest.php
+++ b/core/modules/link/tests/src/Unit/Plugin/migrate/process/d6/FieldLinkTest.php
@@ -58,6 +58,10 @@ public function canonicalizeUriDataProvider() {
         'www.yahoo.com',
         'http://www.yahoo.com',
       ],
+      'Absolute URL without protocol prefix nor www' => [
+        'yahoo.com',
+        'http://yahoo.com',
+      ],
     ];
   }