diff --git a/resources/functionMap.php b/resources/functionMap.php
index bf078bc8a0..8f9d6e9bd0 100644
--- a/resources/functionMap.php
+++ b/resources/functionMap.php
@@ -6312,7 +6312,7 @@
 'mb_check_encoding' => ['bool', 'var='=>'string|array<string>', 'encoding='=>'string'],
 'mb_chr' => ['string|false', 'cp'=>'int', 'encoding='=>'string'],
 'mb_convert_case' => ['string', 'sourcestring'=>'string', 'mode'=>'int', 'encoding='=>'string'],
-'mb_convert_encoding' => ['string|array<int, string>|false', 'val'=>'string|array<int, string>', 'to_encoding'=>'string', 'from_encoding='=>'mixed'],
+'mb_convert_encoding' => ['string|array|false', 'val'=>'string|array<scalar|null|array<scalar|null>>', 'to_encoding'=>'string', 'from_encoding='=>'mixed'],
 'mb_convert_kana' => ['string', 'str'=>'string', 'option='=>'string', 'encoding='=>'string'],
 'mb_convert_variables' => ['string|false', 'to_encoding'=>'string', 'from_encoding'=>'array|string', '&rw_vars'=>'string|array|object', '&...rw_vars='=>'string|array|object'],
 'mb_decode_mimeheader' => ['string', 'string'=>'string'],
diff --git a/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php b/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
index dd46ed4c2a..455962777d 100644
--- a/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
+++ b/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
@@ -5,11 +5,10 @@
 use PhpParser\Node\Expr\FuncCall;
 use PHPStan\Analyser\Scope;
 use PHPStan\Reflection\FunctionReflection;
-use PHPStan\Type\ArrayType;
+use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\DynamicFunctionReturnTypeExtension;
-use PHPStan\Type\IntegerType;
-use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
+use PHPStan\Type\UnionType;
 
 final class MbConvertEncodingFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
 {
@@ -25,18 +24,16 @@ public function getTypeFromFunctionCall(
 		Scope $scope,
 	): ?Type
 	{
-		if (!isset($functionCall->getArgs()[0])) {
+		$args = $functionCall->getArgs();
+		if (!isset($args[0])) {
 			return null;
 		}
 
-		$argType = $scope->getType($functionCall->getArgs()[0]->value);
+		$argType = $scope->getType($args[0]->value);
 		$isString = $argType->isString();
 		$isArray = $argType->isArray();
-		$compare = $isString->compareTo($isArray);
-		if ($compare === $isString) {
-			return new StringType();
-		} elseif ($compare === $isArray) {
-			return new ArrayType(new IntegerType(), new StringType());
+		if ($isString->yes() || $isArray->yes()) {
+			return new UnionType([$argType, new ConstantBooleanType(false)]);
 		}
 
 		return null;
diff --git a/tests/PHPStan/Analyser/nsrt/bug-3336.php b/tests/PHPStan/Analyser/nsrt/bug-3336.php
deleted file mode 100644
index a6712e6f69..0000000000
--- a/tests/PHPStan/Analyser/nsrt/bug-3336.php
+++ /dev/null
@@ -1,10 +0,0 @@
-<?php // lint < 8.0
-
-namespace Bug3336;
-
-function (array $arr, string $str, $mixed): void {
-	\PHPStan\Testing\assertType('array<int, string>', mb_convert_encoding($arr));
-	\PHPStan\Testing\assertType('string', mb_convert_encoding($str));
-	\PHPStan\Testing\assertType('array<int, string>|string|false', mb_convert_encoding($mixed));
-	\PHPStan\Testing\assertType('array<int, string>|string|false', mb_convert_encoding());
-};
diff --git a/tests/PHPStan/Analyser/nsrt/mb_convert_encoding.php b/tests/PHPStan/Analyser/nsrt/mb_convert_encoding.php
new file mode 100644
index 0000000000..37ca6921f9
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/mb_convert_encoding.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace PHPStan\Analyser\nsrt\mb_convert_encoding;
+
+/**
+ * @param array{foo: string, bar: int} $structuredArray
+ * @param list<string> $stringList
+ * @param list<int> $intList
+ */
+function test_mb_convert_encoding(
+	mixed $mixed,
+	string $string,
+	array $mixedArray,
+	array $structuredArray,
+	array $stringList,
+	array $intList,
+): void {
+	\PHPStan\Testing\assertType('array|string|false', mb_convert_encoding($mixed, 'UTF-8'));
+	\PHPStan\Testing\assertType('string|false', mb_convert_encoding($string, 'UTF-8'));
+	\PHPStan\Testing\assertType('array|false', mb_convert_encoding($mixedArray, 'UTF-8'));
+	\PHPStan\Testing\assertType('array{foo: string, bar: int}|false', mb_convert_encoding($structuredArray, 'UTF-8'));
+	\PHPStan\Testing\assertType('list<string>|false', mb_convert_encoding($stringList, 'UTF-8'));
+	\PHPStan\Testing\assertType('list<int>|false', mb_convert_encoding($intList, 'UTF-8'));
+};
+