diff --git a/src/Php/PhpVersion.php b/src/Php/PhpVersion.php
index 6a555dff73..65db8bdae6 100644
--- a/src/Php/PhpVersion.php
+++ b/src/Php/PhpVersion.php
@@ -492,4 +492,9 @@ public function deprecatesIncOnNonNumericString(): bool
 		return $this->versionId >= 80500;
 	}
 
+	public function supportsObjectsInArraySumProduct(): bool
+	{
+		return $this->versionId >= 80300;
+	}
+
 }
diff --git a/src/Rules/Functions/ParameterCastableToNumberRule.php b/src/Rules/Functions/ParameterCastableToNumberRule.php
index 640c73a440..3137688835 100644
--- a/src/Rules/Functions/ParameterCastableToNumberRule.php
+++ b/src/Rules/Functions/ParameterCastableToNumberRule.php
@@ -5,10 +5,12 @@
 use PhpParser\Node;
 use PhpParser\Node\Expr\FuncCall;
 use PHPStan\Analyser\Scope;
+use PHPStan\Php\PhpVersion;
 use PHPStan\Reflection\ParametersAcceptorSelector;
 use PHPStan\Reflection\ReflectionProvider;
 use PHPStan\Rules\ParameterCastableToStringCheck;
 use PHPStan\Rules\Rule;
+use PHPStan\Type\ErrorType;
 use PHPStan\Type\Type;
 use function count;
 use function in_array;
@@ -22,6 +24,7 @@ final class ParameterCastableToNumberRule implements Rule
 	public function __construct(
 		private ReflectionProvider $reflectionProvider,
 		private ParameterCastableToStringCheck $parameterCastableToStringCheck,
+		private PhpVersion $phpVersion,
 	)
 	{
 	}
@@ -63,11 +66,16 @@ public function processNode(Node $node, Scope $scope): array
 
 		$errorMessage = 'Parameter %s of function %s expects an array of values castable to number, %s given.';
 		$functionParameters = $parametersAcceptor->getParameters();
+
+		$castFn = $this->phpVersion->supportsObjectsInArraySumProduct()
+			? static fn (Type $t) => $t->toNumber()
+			: static fn (Type $t) => !$t->isObject()->no() ? new ErrorType() : $t->toNumber();
+
 		$error = $this->parameterCastableToStringCheck->checkParameter(
 			$origArgs[0],
 			$scope,
 			$errorMessage,
-			static fn (Type $t) => $t->toNumber(),
+			$castFn,
 			$functionName,
 			$this->parameterCastableToStringCheck->getParameterName(
 				$origArgs[0],
diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index 85fcc4bf05..8e295b9fc4 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -752,7 +752,10 @@ private function describeCache(): string
 
 	public function toNumber(): Type
 	{
-		if ($this->isInstanceOf('SimpleXMLElement')->yes()) {
+		if (
+			$this->isInstanceOf('SimpleXMLElement')->yes()
+			|| $this->isInstanceOf('GMP')->yes()
+		) {
 			return new UnionType([
 				new FloatType(),
 				new IntegerType(),
diff --git a/tests/PHPStan/Rules/Functions/ParameterCastableToNumberRuleTest.php b/tests/PHPStan/Rules/Functions/ParameterCastableToNumberRuleTest.php
index 588c845952..e4ebd5c149 100644
--- a/tests/PHPStan/Rules/Functions/ParameterCastableToNumberRuleTest.php
+++ b/tests/PHPStan/Rules/Functions/ParameterCastableToNumberRuleTest.php
@@ -2,6 +2,7 @@
 
 namespace PHPStan\Rules\Functions;
 
+use PHPStan\Php\PhpVersion;
 use PHPStan\Rules\ParameterCastableToStringCheck;
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleLevelHelper;
@@ -20,7 +21,11 @@ class ParameterCastableToNumberRuleTest extends RuleTestCase
 	protected function getRule(): Rule
 	{
 		$broker = self::createReflectionProvider();
-		return new ParameterCastableToNumberRule($broker, new ParameterCastableToStringCheck(new RuleLevelHelper($broker, true, false, true, true, true, false, true)));
+		return new ParameterCastableToNumberRule(
+			$broker,
+			new ParameterCastableToStringCheck(new RuleLevelHelper($broker, true, false, true, true, true, false, true)),
+			self::getContainer()->getByType(PhpVersion::class),
+		);
 	}
 
 	public function testRule(): void
@@ -122,6 +127,92 @@ public function testBug11883(): void
 		]);
 	}
 
+	public function testBug13775(): void
+	{
+		$errors = [
+			[
+				'Parameter #1 $array of function array_product expects an array of values castable to number, array<int, string> given.',
+				13,
+			],
+			[
+				'Parameter #1 $array of function array_product expects an array of values castable to number, array<int, string> given.',
+				19,
+			],
+			[
+				'Parameter #1 $array of function array_product expects an array of values castable to number, array<int, string> given.',
+				22,
+			],
+			[
+				'Parameter #1 $array of function array_product expects an array of values castable to number, array<int, string> given.',
+				25,
+			],
+			[
+				'Parameter #1 $array of function array_product expects an array of values castable to number, array<int, array> given.',
+				28,
+			],
+			[
+				'Parameter #1 $array of function array_product expects an array of values castable to number, array<int, stdClass> given.',
+				31,
+			],
+			[
+				'Parameter #1 $array of function array_product expects an array of values castable to number, array<int, GMP|stdClass> given.',
+				34,
+			],
+		];
+
+		if (PHP_VERSION_ID < 80300) {
+			$errors[] = [
+				'Parameter #1 $array of function array_product expects an array of values castable to number, array<int, GMP> given.',
+				37,
+			];
+		}
+
+		$this->analyse([__DIR__ . '/data/bug-13775.php'], $this->hackPhp74ErrorMessages($errors));
+	}
+
+	public function testBug13775Bis(): void
+	{
+		$errors = [
+			[
+				'Parameter #1 $array of function array_sum expects an array of values castable to number, array<int, string> given.',
+				13,
+			],
+			[
+				'Parameter #1 $array of function array_sum expects an array of values castable to number, array<int, string> given.',
+				19,
+			],
+			[
+				'Parameter #1 $array of function array_sum expects an array of values castable to number, array<int, string> given.',
+				22,
+			],
+			[
+				'Parameter #1 $array of function array_sum expects an array of values castable to number, array<int, string> given.',
+				25,
+			],
+			[
+				'Parameter #1 $array of function array_sum expects an array of values castable to number, array<int, array> given.',
+				28,
+			],
+			[
+				'Parameter #1 $array of function array_sum expects an array of values castable to number, array<int, stdClass> given.',
+				31,
+			],
+			[
+				'Parameter #1 $array of function array_sum expects an array of values castable to number, array<int, GMP|stdClass> given.',
+				34,
+			],
+		];
+
+		if (PHP_VERSION_ID < 80300) {
+			$errors[] = [
+				'Parameter #1 $array of function array_sum expects an array of values castable to number, array<int, GMP> given.',
+				37,
+			];
+		}
+
+		$this->analyse([__DIR__ . '/data/bug-13775-bis.php'], $this->hackPhp74ErrorMessages($errors));
+	}
+
 	public function testBug12146(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-12146.php'], $this->hackPhp74ErrorMessages([
diff --git a/tests/PHPStan/Rules/Functions/data/bug-13775-bis.php b/tests/PHPStan/Rules/Functions/data/bug-13775-bis.php
new file mode 100644
index 0000000000..69890599fa
--- /dev/null
+++ b/tests/PHPStan/Rules/Functions/data/bug-13775-bis.php
@@ -0,0 +1,37 @@
+<?php declare(strict_types = 1);
+
+$a = [null];
+echo 'null, valid cast: ' . array_sum($a) . "\n\n";
+
+$a = [false];
+echo 'false, valid cast: ' . array_sum($a) . "\n\n";
+
+$a = [true];
+echo 'true, valid cast: ' . array_sum($a) . "\n\n";
+
+$a = [''];
+echo 'empty string, invalid cast: ' . array_sum($a) . "\n\n";
+
+$a = ['42.5'];
+echo 'string of a float, valid cast: ' . array_sum($a) . "\n\n";
+
+$a = ['42,5'];
+echo 'string of comma-separated float, valid cast but not desirable (discards trailing chars): ' . array_sum($a) . "\n\n";
+
+$a = ['42a'];
+echo 'string of int with trailing alpha char, valid cast but not desirable (discards trailing chars): ' . array_sum($a) . "\n\n";
+
+$a = ['a42'];
+echo 'string of int with leading alpha char, invalid cast: ' . array_sum($a) . "\n\n";
+
+$a = [[]];
+echo 'array, invalid cast: ' . array_sum($a) . "\n\n";
+
+$a = [new stdClass()];
+echo 'class that does not auto-cast, invalid cast: ' . array_sum($a) . "\n\n";
+
+$a = [rand(0, 1) ? new stdClass() : gmp_init(42)];
+echo 'possibly invalid cast: ' . array_sum($a) . "\n\n";
+
+$a = [gmp_init(42)];
+echo 'gmp, valid cast: ' . array_sum($a) . "\n\n";
diff --git a/tests/PHPStan/Rules/Functions/data/bug-13775.php b/tests/PHPStan/Rules/Functions/data/bug-13775.php
new file mode 100644
index 0000000000..04d4fd06b8
--- /dev/null
+++ b/tests/PHPStan/Rules/Functions/data/bug-13775.php
@@ -0,0 +1,37 @@
+<?php declare(strict_types = 1);
+
+$a = [null];
+echo 'null, valid cast: ' . array_product($a) . "\n\n";
+
+$a = [false];
+echo 'false, valid cast: ' . array_product($a) . "\n\n";
+
+$a = [true];
+echo 'true, valid cast: ' . array_product($a) . "\n\n";
+
+$a = [''];
+echo 'empty string, invalid cast: ' . array_product($a) . "\n\n";
+
+$a = ['42.5'];
+echo 'string of a float, valid cast: ' . array_product($a) . "\n\n";
+
+$a = ['42,5'];
+echo 'string of comma-separated float, valid cast but not desirable (discards trailing chars): ' . array_product($a) . "\n\n";
+
+$a = ['42a'];
+echo 'string of int with trailing alpha char, valid cast but not desirable (discards trailing chars): ' . array_product($a) . "\n\n";
+
+$a = ['a42'];
+echo 'string of int with leading alpha char, invalid cast: ' . array_product($a) . "\n\n";
+
+$a = [[]];
+echo 'array, invalid cast: ' . array_product($a) . "\n\n";
+
+$a = [new stdClass()];
+echo 'class that does not auto-cast, invalid cast: ' . array_product($a) . "\n\n";
+
+$a = [rand(0, 1) ? new stdClass() : gmp_init(42)];
+echo 'possibly invalid cast: ' . array_product($a) . "\n\n";
+
+$a = [gmp_init(42)];
+echo 'gmp, valid cast: ' . array_product($a) . "\n\n";
diff --git a/tests/PHPStan/Rules/Functions/data/param-castable-to-number-functions.php b/tests/PHPStan/Rules/Functions/data/param-castable-to-number-functions.php
index 9e7c5da4d2..b744bc35eb 100644
--- a/tests/PHPStan/Rules/Functions/data/param-castable-to-number-functions.php
+++ b/tests/PHPStan/Rules/Functions/data/param-castable-to-number-functions.php
@@ -40,6 +40,6 @@ function wrongNumberOfArguments(): void
 
 function validUsages(): void
 {
-	var_dump(array_sum(['5.5', false, true, new \SimpleXMLElement('<a>7.7</a>'), 5, 5.5, null]));
-	var_dump(array_product(['5.5', false, true, new \SimpleXMLElement('<a>7.7</a>'), 5, 5.5, null]));
+	var_dump(array_sum(['5.5', false, true, 5, 5.5, null]));
+	var_dump(array_product(['5.5', false, true, 5, 5.5, null]));
 }
diff --git a/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php b/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
index bfca28ee4f..fb1b119745 100644
--- a/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
+++ b/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
@@ -795,6 +795,13 @@ public function testBenevolentUnion(): void
 		]);
 	}
 
+	public function testBug12123(): void
+	{
+		$this->checkImplicitMixed = true;
+
+		$this->analyse([__DIR__ . '/data/bug-12123.php'], []);
+	}
+
 	public function testBug7863(): void
 	{
 		$this->checkImplicitMixed = true;
diff --git a/tests/PHPStan/Rules/Operators/data/bug-12123.php b/tests/PHPStan/Rules/Operators/data/bug-12123.php
new file mode 100644
index 0000000000..13ba245955
--- /dev/null
+++ b/tests/PHPStan/Rules/Operators/data/bug-12123.php
@@ -0,0 +1,7 @@
+<?php declare(strict_types = 1);
+
+namespace Bug12123;
+
+$x = gmp_init('1');
+$y = $x * 2;
+var_dump($y);