diff --git a/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php b/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
index a09f0a823a..7878ba704e 100644
--- a/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
+++ b/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
@@ -4,6 +4,7 @@
 
 use PhpParser\Node\Expr\FuncCall;
 use PHPStan\Analyser\Scope;
+use PHPStan\Php\PhpVersion;
 use PHPStan\Reflection\FunctionReflection;
 use PHPStan\Reflection\ParametersAcceptorSelector;
 use PHPStan\Type\Accessory\AccessoryArrayListType;
@@ -17,10 +18,15 @@
 use PHPStan\Type\TypeCombinator;
 use PHPStan\Type\UnionType;
 use function count;
+use function str_contains;
 
 final class MbConvertEncodingFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
 {
 
+	public function __construct(private PhpVersion $phpVersion)
+	{
+	}
+
 	public function isFunctionSupported(FunctionReflection $functionReflection): bool
 	{
 		return $functionReflection->getName() === 'mb_convert_encoding';
@@ -46,7 +52,46 @@ public function getTypeFromFunctionCall(
 
 		$result = TypeCombinator::intersect($initialReturnType, $this->generalizeStringType($argType));
 		if ($result instanceof NeverType) {
-			return null;
+			$result = $initialReturnType;
+		}
+
+		if ($this->phpVersion->throwsValueErrorForInternalFunctions()) {
+			if (!isset($functionCall->getArgs()[2])) {
+				return TypeCombinator::remove($result, new ConstantBooleanType(false));
+			}
+			$fromEncodingArgType = $scope->getType($functionCall->getArgs()[2]->value);
+
+			$returnFalseIfCannotDetectEncoding = false;
+			if (!$fromEncodingArgType->isArray()->no()) {
+				$constantArrays = $fromEncodingArgType->getConstantArrays();
+				if (count($constantArrays) > 0) {
+					foreach ($constantArrays as $constantArray) {
+						if (count($constantArray->getValueTypes()) > 1) {
+							$returnFalseIfCannotDetectEncoding = true;
+							break;
+						}
+					}
+				} else {
+					$returnFalseIfCannotDetectEncoding = true;
+				}
+			}
+			if (!$returnFalseIfCannotDetectEncoding && !$fromEncodingArgType->isString()->no()) {
+				$constantStrings = $fromEncodingArgType->getConstantStrings();
+				if (count($constantStrings) > 0) {
+					foreach ($constantStrings as $constantString) {
+						if (str_contains($constantString->getValue(), ',')) {
+							$returnFalseIfCannotDetectEncoding = true;
+							break;
+						}
+					}
+				} else {
+					$returnFalseIfCannotDetectEncoding = true;
+				}
+			}
+
+			if (!$returnFalseIfCannotDetectEncoding) {
+				return TypeCombinator::remove($result, new ConstantBooleanType(false));
+			}
 		}
 
 		return TypeCombinator::union($result, new ConstantBooleanType(false));
diff --git a/tests/PHPStan/Analyser/nsrt/mb_convert_encoding.php b/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php7.php
similarity index 96%
rename from tests/PHPStan/Analyser/nsrt/mb_convert_encoding.php
rename to tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php7.php
index f5f524d44f..d1de6c7c24 100644
--- a/tests/PHPStan/Analyser/nsrt/mb_convert_encoding.php
+++ b/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php7.php
@@ -1,6 +1,6 @@
-<?php
+<?php // lint <= 8.0
 
-namespace MbConvertEncoding;
+namespace MbConvertEncodingPHP7;
 
 /**
  * @param 'foo'|'bar' $constantString
diff --git a/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php8.php b/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php8.php
new file mode 100644
index 0000000000..a4d4121e18
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php8.php
@@ -0,0 +1,45 @@
+<?php // lint >= 8.0
+
+namespace MbConvertEncodingPHP8;
+
+/**
+ * @param 'foo'|'bar' $constantString
+ * @param array{foo: string, bar: int, baz: 'foo'} $structuredArray
+ * @param list<string> $stringList
+ * @param list<int> $intList
+ * @param 'foo'|'bar'|array{foo: string, bar: int, baz: 'foo'}|bool $union
+ */
+function test_mb_convert_encoding(
+	mixed $mixed,
+	string $constantString,
+	string $string,
+	array $mixedArray,
+	array $structuredArray,
+	array $stringList,
+	array $intList,
+	string|array|bool $union,
+	int $int,
+): void {
+	\PHPStan\Testing\assertType('array|string', mb_convert_encoding($mixed, 'UTF-8'));
+	\PHPStan\Testing\assertType('string', mb_convert_encoding($constantString, 'UTF-8'));
+	\PHPStan\Testing\assertType('string', mb_convert_encoding($string, 'UTF-8'));
+	\PHPStan\Testing\assertType('array', mb_convert_encoding($mixedArray, 'UTF-8'));
+	\PHPStan\Testing\assertType('array{foo: string, bar: int, baz: string}', mb_convert_encoding($structuredArray, 'UTF-8'));
+	\PHPStan\Testing\assertType('list<string>', mb_convert_encoding($stringList, 'UTF-8'));
+	\PHPStan\Testing\assertType('list<int>', mb_convert_encoding($intList, 'UTF-8'));
+	\PHPStan\Testing\assertType('array{foo: string, bar: int, baz: string}|string', mb_convert_encoding($union, 'UTF-8'));
+	\PHPStan\Testing\assertType('array|string', mb_convert_encoding($int, 'UTF-8'));
+
+	\PHPStan\Testing\assertType('string', mb_convert_encoding($string, 'UTF-8', 'FOO'));
+	\PHPStan\Testing\assertType('string|false', mb_convert_encoding($string, 'UTF-8', $string));
+	\PHPStan\Testing\assertType('string|false', mb_convert_encoding($string, 'UTF-8', 'FOO,BAR'));
+	\PHPStan\Testing\assertType('string', mb_convert_encoding($string, 'UTF-8', ['FOO']));
+	\PHPStan\Testing\assertType('string|false', mb_convert_encoding($string, 'UTF-8', ['FOO', 'BAR']));
+	\PHPStan\Testing\assertType('string', mb_convert_encoding($string, 'UTF-8', ['FOO,BAR']));
+	\PHPStan\Testing\assertType('list<string>', mb_convert_encoding($stringList, 'UTF-8', 'FOO'));
+	\PHPStan\Testing\assertType('list<string>|false', mb_convert_encoding($stringList, 'UTF-8', $string));
+	\PHPStan\Testing\assertType('list<string>|false', mb_convert_encoding($stringList, 'UTF-8', 'FOO,BAR'));
+	\PHPStan\Testing\assertType('list<string>', mb_convert_encoding($stringList, 'UTF-8', ['FOO']));
+	\PHPStan\Testing\assertType('list<string>|false', mb_convert_encoding($stringList, 'UTF-8', ['FOO', 'BAR']));
+	\PHPStan\Testing\assertType('list<string>', mb_convert_encoding($stringList, 'UTF-8', ['FOO,BAR']));
+};