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'));