diff --git a/src/Carbon/Traits/Date.php b/src/Carbon/Traits/Date.php
index 43ca171b6c..65433bbca8 100644
--- a/src/Carbon/Traits/Date.php
+++ b/src/Carbon/Traits/Date.php
@@ -2967,6 +2967,6 @@ private function mutateIfMutable(CarbonInterface $date): CarbonInterface
     {
         return $this instanceof DateTimeImmutable
             ? $this
-            : $this->modify('@' . $date->rawFormat('U.u'))->setTimezone($date->getTimezone());
+            : $this->modify('@'.$date->rawFormat('U.u'))->setTimezone($date->getTimezone());
     }
 }
diff --git a/tests/Carbon/SettersTest.php b/tests/Carbon/SettersTest.php
index 11017205a4..e816339574 100644
--- a/tests/Carbon/SettersTest.php
+++ b/tests/Carbon/SettersTest.php
@@ -658,7 +658,7 @@ public function testSetUnitNoOverflow()
                 'microsecond' => 1000000,
             ];
             $valueUnit = array_keys($units)[mt_rand(0, \count($units) - 1)];
-            $value = mt_rand() > 0.5 ?
+            $value = mt_rand(0, 1) === 1 ?
                 mt_rand(-9999, 9999) :
                 mt_rand(-60, 60);
 
@@ -803,7 +803,7 @@ public function testAddUnitNoOverflow()
                 'microsecond' => 1000000,
             ];
             $valueUnit = array_keys($units)[mt_rand(0, \count($units) - 1)];
-            $value = mt_rand() > 0.5 ?
+            $value = mt_rand(0, 1) === 1 ?
                 mt_rand(-9999, 9999) :
                 mt_rand(-60, 60);
 
@@ -840,8 +840,7 @@ public function testAddUnitNoOverflow()
             }
             if ($value === $date->$valueUnit ||
                 $modulo === $date->$valueUnit ||
-                (method_exists($date, "diffInReal$unit") && -$date->{"diffInReal$unit"}($original, false) === $value) ||
-                -((int) round($date->{"diffIn$unit"}($original, false))) === $value
+                (method_exists($date, "diffInReal$unit") && -$date->{"diffInReal$unit"}($original, false) === $value)
             ) {
                 $results['current']++;
 
@@ -860,6 +859,33 @@ public function testAddUnitNoOverflow()
                 continue;
             }
 
+            $currentDiff = -((int) round($date->{"diffIn$unit"}($original, false)));
+
+            if ($currentDiff === $value) {
+                $results['current']++;
+
+                continue;
+            }
+
+            $delta = ($currentDiff - $value);
+
+            if ($valueUnit === 'hour') {
+                $diff = $this->getOffsetChangeOfTheDay($date) ?: $this->getOffsetChangeOfTheDay($original);
+
+                if ($diff !== 0) {
+                    $sign = $diff < 0 ? -1 : 1;
+                    $diff = abs($diff);
+                    $minutes = $diff % 100;
+                    $hours = (int) ($sign * (floor($diff / 100) + $minutes / 60));
+
+                    if ($delta === -$hours) {
+                        $results['current']++;
+
+                        continue;
+                    }
+                }
+            }
+
             $this->failOperation(
                 $original,
                 $date,
@@ -912,7 +938,7 @@ public function testSubUnitNoOverflow()
                 'microsecond' => 1000000,
             ];
             $valueUnit = array_keys($units)[mt_rand(0, \count($units) - 1)];
-            $value = mt_rand() > 0.5 ?
+            $value = mt_rand(0, 1) === 1 ?
                 mt_rand(-9999, 9999) :
                 mt_rand(-60, 60);
 
@@ -951,8 +977,7 @@ public function testSubUnitNoOverflow()
 
             if ($value === $date->$valueUnit ||
                 $modulo === $date->$valueUnit ||
-                (method_exists($date, "diffInReal$unit") && $value === $date->{"diffInReal$unit"}($original, false)) ||
-                ((int) round($date->{"diffIn$unit"}($original, false))) === $value
+                (method_exists($date, "diffInReal$unit") && $value === $date->{"diffInReal$unit"}($original, false))
             ) {
                 $results['current']++;
 
@@ -986,6 +1011,33 @@ public function testSubUnitNoOverflow()
                 continue;
             }
 
+            $currentDiff = (int) round($date->{"diffIn$unit"}($original, false));
+
+            if ($currentDiff === $value) {
+                $results['current']++;
+
+                continue;
+            }
+
+            $delta = ($currentDiff - $value);
+
+            if ($valueUnit === 'hour') {
+                $diff = $this->getOffsetChangeOfTheDay($date) ?: $this->getOffsetChangeOfTheDay($original);
+
+                if ($diff !== 0) {
+                    $sign = $diff < 0 ? -1 : 1;
+                    $diff = abs($diff);
+                    $minutes = $diff % 100;
+                    $hours = (int) ($sign * (floor($diff / 100) + $minutes / 60));
+
+                    if ($delta === $hours) {
+                        $results['current']++;
+
+                        continue;
+                    }
+                }
+            }
+
             $this->failOperation(
                 $original,
                 $date,
@@ -998,6 +1050,8 @@ public function testSubUnitNoOverflow()
                 $unit,
                 $modulo,
                 $value,
+                $hours ?? null,
+                $delta ?? null,
             );
         }
 
@@ -1011,13 +1065,32 @@ public function testSubUnitNoOverflow()
 
     public function testOverflowInDst()
     {
-        $date = Carbon::create(2335, 11, 3, 1, 30, 50.138159);
-        $date->subUnitNoOverflow('year', 5668, 'second');
+        $date = Carbon::create(2335, 11, 3, 1, 30, 50.138159)
+            ->subUnitNoOverflow('year', 5668, 'second');
 
         $this->assertSame(
             '2335-11-03 01:30:50.000000 America/Toronto -0400',
             $date->format('Y-m-d H:i:s.u e O'),
         );
+
+        $date = Carbon::parse('2020-10-15 03:22:57.442989', 'America/Toronto')->hours(-5302);
+
+        $diff = (int) ($date->copy()->startOfDay()->format('O') - $date->copy()->endOfDay()->format('O'));
+        $sign = $diff < 0 ? -1 : 1;
+        $diff = abs($diff);
+        $minutes = $diff % 100;
+        $hours = $sign * (floor($diff / 100) + $minutes / 60);
+
+        $diffInHours = $date->diffInHours(
+            Carbon::parse('2020-10-15 03:22:57.442989', 'America/Toronto'),
+        );
+
+        $this->assertSame(5305.0 + $hours, $diffInHours);
+    }
+
+    private function getOffsetChangeOfTheDay(Carbon $date): int
+    {
+        return (int) ($date->copy()->startOfDay()->format('O') - $date->copy()->endOfDay()->format('O'));
     }
 
     /**
@@ -1034,7 +1107,9 @@ private function failOperation(
         string $overflowUnit,
         string $unit,
         int $modulo,
-        int $variableValue
+        int $variableValue,
+        ?int $hours = null,
+        ?int $delta = null,
     ): void {
         throw new Exception(implode("\n", [
             'Unhandled result for: '.
@@ -1049,6 +1124,9 @@ private function failOperation(
             'Nor '.$end->$valueUnit." (from $end)",
             "Nor $value (from value)",
             "Nor $modulo (from modulo)",
+            ...($hours !== null ? [
+                "Not matching diff (hours = $hours vs delta = " . ($delta ?? 'null') . ')',
+            ] : []),
             method_exists($date, "diffInReal$unit")
                 ? "diffInReal$unit() exists and returns ".$date->{"diffInReal$unit"}($original, false)
                     ." while expecting $variableValue"