diff --git a/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php b/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
index f567eadfb6..f12efd095c 100644
--- a/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
+++ b/src/Type/Php/MbConvertEncodingFunctionReturnTypeExtension.php
@@ -20,6 +20,8 @@
 use PHPStan\Type\UnionType;
 use function count;
 use function str_contains;
+use function strtolower;
+use function trim;
 
 #[AutowiredService]
 final class MbConvertEncodingFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
@@ -81,7 +83,10 @@ public function getTypeFromFunctionCall(
 				$constantStrings = $fromEncodingArgType->getConstantStrings();
 				if (count($constantStrings) > 0) {
 					foreach ($constantStrings as $constantString) {
-						if (str_contains($constantString->getValue(), ',')) {
+						if (
+							str_contains($constantString->getValue(), ',')
+							|| trim(strtolower($constantString->getValue())) === 'auto'
+						) {
 							$returnFalseIfCannotDetectEncoding = true;
 							break;
 						}
diff --git a/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php7.php b/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php7.php
index d1de6c7c24..2fb84826f9 100644
--- a/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php7.php
+++ b/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php7.php
@@ -29,4 +29,7 @@ function test_mb_convert_encoding(
 	\PHPStan\Testing\assertType('list<int>|false', mb_convert_encoding($intList, 'UTF-8'));
 	\PHPStan\Testing\assertType('array{foo: string, bar: int, baz: string}|string|false', mb_convert_encoding($union, 'UTF-8'));
 	\PHPStan\Testing\assertType('array|string|false', mb_convert_encoding($int, 'UTF-8'));
+
+	\PHPStan\Testing\assertType('string|false', mb_convert_encoding($string, 'UTF-8', 'auto'));
+	\PHPStan\Testing\assertType('string|false', mb_convert_encoding($string, 'UTF-8', ' AUTO '));
 };
diff --git a/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php8.php b/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php8.php
index a4d4121e18..e96f8f0e1a 100644
--- a/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php8.php
+++ b/tests/PHPStan/Analyser/nsrt/mb-convert-encoding-php8.php
@@ -42,4 +42,7 @@ function test_mb_convert_encoding(
 	\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($stringList, 'UTF-8', ['FOO,BAR']));
+
+	\PHPStan\Testing\assertType('string|false', mb_convert_encoding($string, 'UTF-8', 'auto'));
+	\PHPStan\Testing\assertType('string|false', mb_convert_encoding($string, 'UTF-8', ' AUTO '));
 };