diff --git a/.github/workflows/actions.yml b/.github/workflows/actions.yml
index ac66d212..d1c7c97b 100644
--- a/.github/workflows/actions.yml
+++ b/.github/workflows/actions.yml
@@ -7,7 +7,7 @@ jobs:
     strategy:
       matrix:
         operating-system: [ubuntu-latest]
-        php-versions: ['7.4', '8.0']
+        php-versions: ['7.4', '8.0', '8.1']
 
     runs-on: ${{ matrix.operating-system }}
 
diff --git a/.gitignore b/.gitignore
index 4b72e7ad..82b7dad3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,23 +5,5 @@ tests/cov/
 tests/temp
 tests/.phpunit.result.cache
 
-#vim
-.*.swp
-
-#binaries
-bin/phpunit
-bin/phpcs
-bin/php-cs-fixer
-bin/sabre-cs-fixer
-bin/hoa
-
-# Development stuff
-.php_cs.cache
-.idea
-
-# OS X
-.DS_Store
-=======
-
 # Development stuff
 .php_cs.cache
diff --git a/.php_cs.dist b/.php_cs.dist
index 7c6cf674..4aaf1d90 100644
--- a/.php_cs.dist
+++ b/.php_cs.dist
@@ -6,8 +6,7 @@ $config->getFinder()
     ->in(__DIR__);
 $config->setRules([
     '@PSR1' => true,
-    '@Symfony' => true,
-    'phpdoc_summary' => false
+    '@Symfony' => true
 ]);
 
 return $config;
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 4f50e97f..00000000
--- a/.travis.yml
+++ /dev/null
@@ -1,49 +0,0 @@
-language: php
-php:
-  - 7.1
-  - 7.2
-  - 7.3
-  - 7.4
-
-env:
-  global:
-    - MEMCACHED_SERVER=127.0.0.1
-    - RUN_PHPCSFIXER="TRUE"
-    - RUN_PHPUNIT="TRUE"
-    - RUN_PHPSTAN="FALSE"
-  matrix:
-    - PREFER_LOWEST="" REPORT_COVERAGE="TRUE" WITH_COVERAGE="--coverage-clover=coverage.xml"
-    - PREFER_LOWEST="--prefer-lowest" REPORT_COVERAGE="FALSE" WITH_COVERAGE=""
-
-matrix:
-  include:
-    - name: 'PHP8'
-      dist: focal
-      php: nightly
-      env:
-        - RUN_PHPCSFIXER="FALSE"
-        - REPORT_COVERAGE="FALSE"
-    - name: 'PHPStan'
-      php: 7.4
-      env:
-        - RUN_PHPCSFIXER="FALSE"
-        - RUN_PHPUNIT="FALSE"
-        - RUN_PHPSTAN="TRUE"
-        - REPORT_COVERAGE="FALSE"
-  fast_finish: true
-
-before_script:
-  - if [ $RUN_PHPCSFIXER == "FALSE" ]; then composer remove --no-update --dev friendsofphp/php-cs-fixer; fi
-  - composer update $PREFER_LOWEST
-
-script:
-  - if [ $RUN_PHPCSFIXER == "TRUE" ]; then php vendor/bin/php-cs-fixer fix --dry-run --diff; fi
-  - if [ $RUN_PHPUNIT == "TRUE" ]; then php vendor/bin/phpunit --configuration tests/phpunit.xml $WITH_COVERAGE; fi
-  - if [ $RUN_PHPSTAN == "TRUE" ]; then composer phpstan; fi
-
-after_success:
-  - if [ $REPORT_COVERAGE == "TRUE" ]; then bash <(curl -s https://codecov.io/bash); fi
-
-cache:
-  directories:
-    - $HOME/.composer/cache
diff --git a/lib/Parser/MimeDir.php b/lib/Parser/MimeDir.php
index ecf1944f..9256af6f 100644
--- a/lib/Parser/MimeDir.php
+++ b/lib/Parser/MimeDir.php
@@ -518,7 +518,7 @@ protected function readProperty($line)
      *
      * Now for the parameters
      *
-     * If delimiter is not set (null) this method will just return a string.
+     * If delimiter is not set (empty string) this method will just return a string.
      * If it's a comma or a semi-colon the string will be split on those
      * characters, and always return an array.
      *
diff --git a/lib/Property.php b/lib/Property.php
index 6219c9b6..50cda968 100644
--- a/lib/Property.php
+++ b/lib/Property.php
@@ -52,7 +52,7 @@ abstract class Property extends Node
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
     public $delimiter = ';';
 
diff --git a/lib/Property/Binary.php b/lib/Property/Binary.php
index ec6713fd..1262dd05 100644
--- a/lib/Property/Binary.php
+++ b/lib/Property/Binary.php
@@ -24,9 +24,9 @@ class Binary extends Property
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Updates the current value.
diff --git a/lib/Property/FloatValue.php b/lib/Property/FloatValue.php
index 0d034696..e780ae6c 100644
--- a/lib/Property/FloatValue.php
+++ b/lib/Property/FloatValue.php
@@ -21,7 +21,7 @@ class FloatValue extends Property
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
     public $delimiter = ';';
 
diff --git a/lib/Property/ICalendar/CalAddress.php b/lib/Property/ICalendar/CalAddress.php
index 86be66c1..2dbbc6ea 100644
--- a/lib/Property/ICalendar/CalAddress.php
+++ b/lib/Property/ICalendar/CalAddress.php
@@ -19,9 +19,9 @@ class CalAddress extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/ICalendar/Duration.php b/lib/Property/ICalendar/Duration.php
index 87f00816..e18fe191 100644
--- a/lib/Property/ICalendar/Duration.php
+++ b/lib/Property/ICalendar/Duration.php
@@ -22,7 +22,7 @@ class Duration extends Property
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
     public $delimiter = ',';
 
diff --git a/lib/Property/ICalendar/Period.php b/lib/Property/ICalendar/Period.php
index eb375277..ae8a7891 100644
--- a/lib/Property/ICalendar/Period.php
+++ b/lib/Property/ICalendar/Period.php
@@ -23,7 +23,7 @@ class Period extends Property
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
     public $delimiter = ',';
 
diff --git a/lib/Property/Time.php b/lib/Property/Time.php
index 544b5ced..1b81609a 100644
--- a/lib/Property/Time.php
+++ b/lib/Property/Time.php
@@ -19,9 +19,9 @@ class Time extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/Uri.php b/lib/Property/Uri.php
index 830cd3f1..1ad1fb19 100644
--- a/lib/Property/Uri.php
+++ b/lib/Property/Uri.php
@@ -20,9 +20,9 @@ class Uri extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/UtcOffset.php b/lib/Property/UtcOffset.php
index 248ed40e..04b88447 100644
--- a/lib/Property/UtcOffset.php
+++ b/lib/Property/UtcOffset.php
@@ -17,9 +17,9 @@ class UtcOffset extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/VCard/DateAndOrTime.php b/lib/Property/VCard/DateAndOrTime.php
index 09918b31..7bf79c48 100644
--- a/lib/Property/VCard/DateAndOrTime.php
+++ b/lib/Property/VCard/DateAndOrTime.php
@@ -24,9 +24,9 @@ class DateAndOrTime extends Property
     /**
      * Field separator.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/VCard/TimeStamp.php b/lib/Property/VCard/TimeStamp.php
index fccf2d60..da6ea3d4 100644
--- a/lib/Property/VCard/TimeStamp.php
+++ b/lib/Property/VCard/TimeStamp.php
@@ -21,9 +21,9 @@ class TimeStamp extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Recur/EventIterator.php b/lib/Recur/EventIterator.php
index 310bebe4..61f05d7d 100644
--- a/lib/Recur/EventIterator.php
+++ b/lib/Recur/EventIterator.php
@@ -198,6 +198,7 @@ public function __construct($input, $uid = null, DateTimeZone $timeZone = null)
      *
      * @return DateTimeImmutable
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         if ($this->currentDate) {
@@ -285,6 +286,7 @@ public function getEventObject()
      *
      * @return int
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         // The counter is always 1 ahead.
@@ -297,6 +299,7 @@ public function key()
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         if ($this->counter > Settings::$maxRecurrences && -1 !== Settings::$maxRecurrences) {
@@ -308,7 +311,10 @@ public function valid()
 
     /**
      * Sets the iterator back to the starting point.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->recurIterator->rewind();
@@ -331,7 +337,10 @@ public function rewind()
 
     /**
      * Advances the iterator with one step.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         $this->currentOverriddenEvent = null;
diff --git a/lib/Recur/RDateIterator.php b/lib/Recur/RDateIterator.php
index d117e152..5d56657f 100644
--- a/lib/Recur/RDateIterator.php
+++ b/lib/Recur/RDateIterator.php
@@ -35,6 +35,7 @@ public function __construct($rrule, DateTimeInterface $start)
 
     /* Implementation of the Iterator interface {{{ */
 
+    #[\ReturnTypeWillChange]
     public function current()
     {
         if (!$this->valid()) {
@@ -49,6 +50,7 @@ public function current()
      *
      * @return int
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->counter;
@@ -60,6 +62,7 @@ public function key()
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         return $this->counter <= count($this->dates);
@@ -67,7 +70,10 @@ public function valid()
 
     /**
      * Resets the iterator.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->currentDate = clone $this->startDate;
@@ -76,7 +82,10 @@ public function rewind()
 
     /**
      * Goes on to the next iteration.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         ++$this->counter;
diff --git a/lib/Recur/RRuleIterator.php b/lib/Recur/RRuleIterator.php
index 3dd48342..a1b97ebe 100644
--- a/lib/Recur/RRuleIterator.php
+++ b/lib/Recur/RRuleIterator.php
@@ -37,6 +37,7 @@ public function __construct($rrule, DateTimeInterface $start)
 
     /* Implementation of the Iterator interface {{{ */
 
+    #[\ReturnTypeWillChange]
     public function current()
     {
         if (!$this->valid()) {
@@ -51,6 +52,7 @@ public function current()
      *
      * @return int
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->counter;
@@ -63,6 +65,7 @@ public function key()
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         if (null === $this->currentDate) {
@@ -77,7 +80,10 @@ public function valid()
 
     /**
      * Resets the iterator.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->currentDate = clone $this->startDate;
@@ -88,8 +94,10 @@ public function rewind()
      * Goes on to the next iteration.
      *
      * @param int $amount
+     * @return void
      */
-    public function next($amount = 1)
+    #[\ReturnTypeWillChange]
+    public function next(int $amount = 1)
     {
         // Otherwise, we find the next event in the normal RRULE
         // sequence.
@@ -640,6 +648,9 @@ protected function nextMonthly($amount = 1)
             // This goes to 0 because we need to start counting at the
             // beginning.
             $currentDayOfMonth = 0;
+
+            // For some reason the "until" parameter was not being used here,
+            // that's why the workaround of the 10000 year bug was needed at all
             $currentHourOfMonth = 0;
             $currentMinuteOfMonth = 0;
             $currentSecondOfMonth = 0;
@@ -650,6 +661,10 @@ protected function nextMonthly($amount = 1)
             if ($this->until && $this->currentDate->getTimestamp() >= $this->until->getTimestamp()) {
                 return;
             }
+            // let's stop it before the "until" parameter date
+            if ($this->until && $this->currentDate->getTimestamp() >= $this->until->getTimestamp()) {
+                return;
+            }
 
             // To prevent running this forever (better: until we hit the max date of DateTimeImmutable) we simply
             // stop at 9999-12-31. Looks like the year 10000 problem is not solved in php ....
diff --git a/lib/TimeZoneUtil.php b/lib/TimeZoneUtil.php
index 9e382c65..65f2e6c8 100644
--- a/lib/TimeZoneUtil.php
+++ b/lib/TimeZoneUtil.php
@@ -33,14 +33,6 @@ class TimeZoneUtil
     /** @var TimezoneFinder[] */
     private $timezoneFinders = [];
 
-    // Keeping things for backwards compatibility
-    /**
-     * @var array|null
-     *
-     * @deprecated
-     */
-    public static $map = null;
-
     private function __construct()
     {
         $this->addGuesser('lic', new GuessFromLicEntry());
@@ -128,11 +120,30 @@ public static function addTimezoneFinder(string $key, TimezoneFinder $finder): v
         self::getInstance()->addFinder($key, $finder);
     }
 
+    /**
+     * @param string $tzid
+     * @param false  $failIfUncertain
+     *
+     * @return DateTimeZone
+     */
+    public static function getTimeZone($tzid, Component $vcalendar = null, $failIfUncertain = false)
+    {
+        return self::getInstance()->findTimeZone($tzid, $vcalendar, $failIfUncertain);
+    }
+
     public static function clean(): void
     {
         self::$instance = null;
     }
 
+    // Keeping things for backwards compatibility
+    /**
+     * @var array|null
+     *
+     * @deprecated
+     */
+    public static $map = null;
+
     /**
      * List of microsoft exchange timezone ids.
      *
@@ -168,12 +179,12 @@ public static function clean(): void
         48 => 'Asia/Kabul',
         58 => 'Asia/Yekaterinburg',
         47 => 'Asia/Karachi',
-        23 => 'Asia/Kolkata',
+        23 => 'Asia/Calcutta',
         62 => 'Asia/Kathmandu',
         46 => 'Asia/Almaty',
         71 => 'Asia/Dhaka',
         66 => 'Asia/Colombo',
-        61 => 'Asia/Yangon',
+        61 => 'Asia/Rangoon',
         22 => 'Asia/Bangkok',
         64 => 'Asia/Krasnoyarsk',
         45 => 'Asia/Shanghai',
@@ -198,11 +209,11 @@ public static function clean(): void
         29 => 'Atlantic/Azores',
         53 => 'Atlantic/Cape_Verde',
         30 => 'America/Noronha',
-         8 => 'America/Sao_Paulo', // Best guess
+        8 => 'America/Sao_Paulo', // Best guess
         32 => 'America/Argentina/Buenos_Aires',
         60 => 'America/Godthab',
         28 => 'America/St_Johns',
-         9 => 'America/Halifax',
+        9 => 'America/Halifax',
         33 => 'America/Caracas',
         65 => 'America/Santiago',
         35 => 'America/Bogota',
@@ -222,143 +233,6 @@ public static function clean(): void
     ];
 
     /**
-<<<<<<< HEAD
-     * This method will try to find out the correct timezone for an iCalendar
-     * date-time value.
-     *
-     * You must pass the contents of the TZID parameter, as well as the full
-     * calendar.
-     *
-     * If the lookup fails, this method will return the default PHP timezone
-     * (as configured using date_default_timezone_set, or the date.timezone ini
-     * setting).
-     *
-     * Alternatively, if $failIfUncertain is set to true, it will throw an
-     * exception if we cannot accurately determine the timezone.
-     *
-     * @param string                  $tzid
-     * @param Sabre\VObject\Component $vcalendar
-     *
-     * @return \DateTimeZone
-     */
-    public static function getTimeZone($tzid, Component $vcalendar = null, $failIfUncertain = false)
-    {
-        // First we will just see if the tzid is a support timezone identifier.
-        //
-        // The only exception is if the timezone starts with (. This is to
-        // handle cases where certain microsoft products generate timezone
-        // identifiers that for instance look like:
-        //
-        // (GMT+01.00) Sarajevo/Warsaw/Zagreb
-        //
-        // Since PHP 5.5.10, the first bit will be used as the timezone and
-        // this method will return just GMT+01:00. This is wrong, because it
-        // doesn't take DST into account.
-        $originalTzid = $tzid;
-        if ($tzid && '(' !== $tzid[0]) {
-            // If the timezone is prefixed with a slash we remove the slash for lookup in the maps.
-            if ('/' === $tzid[0]) {
-                $tzid = substr($tzid, 1);
-            }
-            // PHP has a bug that logs PHP warnings even it shouldn't:
-            // https://bugs.php.net/bug.php?id=67881
-            //
-            // That's why we're checking if we'll be able to successfully instantiate
-            // \DateTimeZone() before doing so. Otherwise we could simply instantiate
-            // and catch the exception.
-            $tzIdentifiers = \DateTimeZone::listIdentifiers();
-
-            try {
-                if (
-                    (in_array($tzid, $tzIdentifiers)) ||
-                    (preg_match('/^GMT(\+|-)([0-9]{4})$/', $tzid, $matches)) ||
-                    (in_array($tzid, self::getIdentifiersBC()))
-                ) {
-                    return new \DateTimeZone($tzid);
-                }
-            } catch (\Exception $e) {
-            }
-        }
-
-        self::loadTzMaps();
-
-        // Next, we check if the tzid is somewhere in our tzid map.
-        if (isset(self::$map[$tzid])) {
-            return new \DateTimeZone(self::$map[$tzid]);
-        }
-
-        // If we removed the slash we add it back
-        $tzid = $originalTzid;
-
-        // Some Microsoft products prefix the offset first, so let's strip that off
-        // and see if it is our tzid map.  We don't want to check for this first just
-        // in case there are overrides in our tzid map.
-        if (preg_match('/^\((UTC|GMT)(\+|\-)[\d]{2}\:[\d]{2}\) (.*)/', $tzid, $matches)) {
-            $tzidAlternate = $matches[3];
-            if (isset(self::$map[$tzidAlternate])) {
-                return new \DateTimeZone(self::$map[$tzidAlternate]);
-            }
-        }
-
-        // Maybe the author was hyper-lazy and just included an offset. We
-        // support it, but we aren't happy about it.
-        if (preg_match('/^GMT(\+|-)([0-9]{4})$/', $tzid, $matches)) {
-            // Note that the path in the source will never be taken from PHP 5.5.10
-            // onwards. PHP 5.5.10 supports the "GMT+0100" style of format, so it
-            // already gets returned early in this function. Once we drop support
-            // for versions under PHP 5.5.10, this bit can be taken out of the
-            // source.
-            // @codeCoverageIgnoreStart
-            return new \DateTimeZone('Etc/GMT'.$matches[1].ltrim(substr($matches[2], 0, 2), '0'));
-            // @codeCoverageIgnoreEnd
-        }
-
-        if ($vcalendar) {
-            // If that didn't work, we will scan VTIMEZONE objects
-            foreach ($vcalendar->select('VTIMEZONE') as $vtimezone) {
-                if ((string) $vtimezone->TZID === $tzid) {
-                    // Some clients add 'X-LIC-LOCATION' with the olson name.
-                    if (isset($vtimezone->{'X-LIC-LOCATION'})) {
-                        $lic = (string) $vtimezone->{'X-LIC-LOCATION'};
-
-                        // Libical generators may specify strings like
-                        // "SystemV/EST5EDT". For those we must remove the
-                        // SystemV part.
-                        if ('SystemV/' === substr($lic, 0, 8)) {
-                            $lic = substr($lic, 8);
-                        }
-
-                        return self::getTimeZone($lic, null, $failIfUncertain);
-                    }
-                    // Microsoft may add a magic number, which we also have an
-                    // answer for.
-                    if (isset($vtimezone->{'X-MICROSOFT-CDO-TZID'})) {
-                        $cdoId = (int) $vtimezone->{'X-MICROSOFT-CDO-TZID'}->getValue();
-
-                        // 2 can mean both Europe/Lisbon and Europe/Sarajevo.
-                        if (2 === $cdoId && false !== strpos((string) $vtimezone->TZID, 'Sarajevo')) {
-                            return new \DateTimeZone('Europe/Sarajevo');
-                        }
-
-                        if (isset(self::$microsoftExchangeMap[$cdoId])) {
-                            return new \DateTimeZone(self::$microsoftExchangeMap[$cdoId]);
-                        }
-                    }
-                }
-            }
-        }
-
-        if ($failIfUncertain) {
-            throw new \InvalidArgumentException('We were unable to determine the correct PHP timezone for tzid: '.$tzid);
-        }
-
-        // If we got all the way here, we default to UTC.
-        return new \DateTimeZone(date_default_timezone_get());
-    }
-
-    /**
-=======
->>>>>>> upstream/master
      * This method will load in all the tz mapping information, if it's not yet
      * done.
      *
@@ -396,4 +270,4 @@ public static function getIdentifiersBC()
     {
         return include __DIR__.'/timezonedata/php-bc.php';
     }
-}
+}
\ No newline at end of file
diff --git a/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php b/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
index d8c6d5d3..b5c58f71 100644
--- a/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
+++ b/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
@@ -31,6 +31,12 @@ public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
         if ('(' === $tzid[0]) {
             return null;
         }
+
+        // If the timezone is prefixed with a slash we remove the slash for lookup in the maps.
+        if ('/' === $tzid[0]) {
+            $tzid = substr($tzid, 1);
+        }
+
         // PHP has a bug that logs PHP warnings even it shouldn't:
         // https://bugs.php.net/bug.php?id=67881
         //
diff --git a/lib/TimezoneGuesser/FindFromTimezoneMap.php b/lib/TimezoneGuesser/FindFromTimezoneMap.php
index b52ba6a1..0a6b608b 100644
--- a/lib/TimezoneGuesser/FindFromTimezoneMap.php
+++ b/lib/TimezoneGuesser/FindFromTimezoneMap.php
@@ -59,7 +59,8 @@ private function getTzMaps()
                 include __DIR__.'/../timezonedata/windowszones.php',
                 include __DIR__.'/../timezonedata/lotuszones.php',
                 include __DIR__.'/../timezonedata/exchangezones.php',
-                include __DIR__.'/../timezonedata/php-workaround.php'
+                include __DIR__.'/../timezonedata/php-workaround.php',
+                include __DIR__.'/../timezonedata/extrazones.php'
             );
         }
 
diff --git a/tests/VObject/Recur/FastForwardBeforeTest.php b/tests/VObject/Recur/FastForwardBeforeTest.php
index ba71d23d..3461bd6a 100644
--- a/tests/VObject/Recur/FastForwardBeforeTest.php
+++ b/tests/VObject/Recur/FastForwardBeforeTest.php
@@ -282,39 +282,51 @@ public function testFastForwardBeforeMonthly31thDay()
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new DateTimeZone($timezone)))
             ->setDate(18000, 1, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // march
         $rrule->next();
-        $expected += (29 + 31) * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(18000, 3, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // may
         $rrule->next();
-        $expected += (30 + 31) * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(18000, 5, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // july
         $rrule->next();
-        $expected += (30 + 31) * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(18000, 7, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // august
         $rrule->next();
-        $expected += 31 * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(18000, 8, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // october
         $rrule->next();
-        $expected += (30 + 31) * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(18000, 10, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // december
         $rrule->next();
-        $expected += (30 + 31) * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(18000, 12, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
     }
 
@@ -336,37 +348,52 @@ public function testFastForwardBeforeMonthlyAdvanced()
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // tuesday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(8000, 1, 11)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // wednesday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(8000, 1, 19)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // thursday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(8000, 1, 27)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // monday march
-        $expected += (29 + 10) * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(8000, 3, 6)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // tuesday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(8000, 3, 14)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // wednesday (this month starts on wednesday so that's just the next day)
-        $expected += 1 * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(8000, 3, 15)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // thursday
         $expected += 8 * 24 * 60 * 60;
+        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+            ->setDate(8000, 3, 23)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
     }
diff --git a/tests/VObject/Recur/FastForwardTest.php b/tests/VObject/Recur/FastForwardTest.php
index df912056..7a305b4a 100644
--- a/tests/VObject/Recur/FastForwardTest.php
+++ b/tests/VObject/Recur/FastForwardTest.php
@@ -261,32 +261,45 @@ public function testFastForwardMonthly31thDay()
 
         // march
         $rrule->next();
-        $expected += (29 + 31) * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+            ->setDate(18000, 3, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // may
         $rrule->next();
         $expected += (30 + 31) * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+            ->setDate(18000, 5, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // july
         $rrule->next();
-        $expected += (30 + 31) * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+            ->setDate(18000, 7, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // august
         $rrule->next();
-        $expected += 31 * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+            ->setDate(18000, 8, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // october
         $rrule->next();
-        $expected += (30 + 31) * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+            ->setDate(18000, 10, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // december
         $rrule->next();
-        $expected += (30 + 31) * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+            ->setDate(18000, 12, 31)
+            ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
     }
 
@@ -307,37 +320,51 @@ public function testFastForwardMonthlyAdvanced()
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // tuesday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+            ->setDate(8000, 1, 11)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // wednesday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+            ->setDate(8000, 1, 19)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // thursday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+            ->setDate(8000, 1, 27)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // monday march
-        $expected += (29 + 10) * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+            ->setDate(8000, 3, 6)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // tuesday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+            ->setDate(8000, 3, 14)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // wednesday (this month starts on wednesday so that's just the next day)
-        $expected += 1 * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+            ->setDate(8000, 3, 15)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // thursday
-        $expected += 8 * 24 * 60 * 60;
+        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+            ->setDate(8000, 3, 23)
+            ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
     }
diff --git a/tests/VObject/Recur/FastForwardToEndTest.php b/tests/VObject/Recur/FastForwardToEndTest.php
index 9f54d838..992f2b9d 100644
--- a/tests/VObject/Recur/FastForwardToEndTest.php
+++ b/tests/VObject/Recur/FastForwardToEndTest.php
@@ -186,9 +186,7 @@ public function testFastForwardToEndUntilMonthlyBasic()
     }
 
     /**
-     * FIXME fails in <=PHP 7.1.
-     *
-     * @requires PHP 7.2
+     * @requires PHP < 8.1
      */
     public function testFastForwardToEndCountMonthly31thDay()
     {
@@ -204,6 +202,22 @@ public function testFastForwardToEndCountMonthly31thDay()
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
     }
 
+    /**
+     * @requires PHP >= 8.1
+     */
+    public function testFastForwardToEndCountMonthly31thDayPHP81()
+    {
+        $startDate = new \DateTime('1970-01-31 00:00:00', new \DateTimeZone('America/New_York'));
+        $rrule = new RRuleIterator('FREQ=MONTHLY;COUNT=10000', $startDate);
+
+        // We do not enforce the timing in case of a count rule as we cannot optimize it
+        $this->fastForwardToEnd($rrule, false);
+
+        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+            ->setDate(3398, 7, 31);
+        $this->assertEquals($expected->getTimestamp(), $rrule->current()->getTimestamp());
+    }
+
     public function testFastForwardToEndUntilMonthly31thDay()
     {
         $startDate = new \DateTime('1970-01-31 00:00:00', new \DateTimeZone('America/New_York'));
diff --git a/tests/VObject/TimeZoneUtilTest.php b/tests/VObject/TimeZoneUtilTest.php
index 33a1eff9..e6df79ae 100644
--- a/tests/VObject/TimeZoneUtilTest.php
+++ b/tests/VObject/TimeZoneUtilTest.php
@@ -8,8 +8,6 @@ class TimeZoneUtilTest extends TestCase
 {
     public function setUp(): void
     {
-        // clearning the tz cache
-        TimeZoneUtil::$map = null;
         TimeZoneUtil::clean();
     }
 
@@ -36,7 +34,8 @@ public function getMapping()
             include __DIR__.'/../../lib/timezonedata/windowszones.php',
             include __DIR__.'/../../lib/timezonedata/lotuszones.php',
             include __DIR__.'/../../lib/timezonedata/exchangezones.php',
-            include __DIR__.'/../../lib/timezonedata/php-workaround.php'
+            include __DIR__.'/../../lib/timezonedata/php-workaround.php',
+            include __DIR__.'/../../lib/timezonedata/extrazones.php'
         );
 
         // PHPUNit requires an array of arrays