diff --git a/resources/functionMap.php b/resources/functionMap.php
index 2b31468b37..1308d22342 100644
--- a/resources/functionMap.php
+++ b/resources/functionMap.php
@@ -6318,7 +6318,8 @@
 'mb_decode_mimeheader' => ['string', 'string'=>'string'],
 'mb_decode_numericentity' => ['string', 'string'=>'string', 'convmap'=>'array', 'encoding'=>'string'],
 'mb_detect_encoding' => ['string|false', 'str'=>'string', 'encoding_list='=>'mixed', 'strict='=>'bool'],
-'mb_detect_order' => ['bool|list<non-falsy-string>', 'encoding_list='=>'non-empty-list<non-falsy-string>|non-falsy-string'],
+'mb_detect_order' => ['bool', 'encoding_list'=>'non-empty-list<non-falsy-string>|non-falsy-string'],
+'mb_detect_order\'1' => ['list<non-falsy-string>'],
 'mb_encode_mimeheader' => ['string', 'str'=>'string', 'charset='=>'string', 'transfer_encoding='=>'string', 'linefeed='=>'string', 'indent='=>'int'],
 'mb_encode_numericentity' => ['string', 'string'=>'string', 'convmap'=>'array', 'encoding='=>'string', 'is_hex='=>'bool'],
 'mb_encoding_aliases' => ['list<non-falsy-string>|false', 'encoding'=>'string'],
diff --git a/resources/functionMap_php80delta.php b/resources/functionMap_php80delta.php
index f37e4e3b93..a972ac4f51 100644
--- a/resources/functionMap_php80delta.php
+++ b/resources/functionMap_php80delta.php
@@ -86,7 +86,8 @@
 		'getenv\'1' => ['array<string, string>', 'varname='=>'null', 'local_only='=>'bool'],
 		'ldap_set_rebind_proc' => ['bool', 'ldap'=>'resource', 'callback'=>'?callable'],
 		'mb_decode_numericentity' => ['string|false', 'string'=>'string', 'convmap'=>'array', 'encoding='=>'string'],
-		'mb_detect_order' => ['bool|list<non-falsy-string>', 'encoding_list='=>'non-empty-list<non-falsy-string>|non-falsy-string|null'],
+		'mb_detect_order' => ['bool', 'encoding_list'=>'non-empty-list<non-falsy-string>|non-falsy-string'],
+		'mb_detect_order\'1' => ['list<non-falsy-string>', 'encoding_list='=>'null'],
 		'mb_encoding_aliases' => ['list<non-falsy-string>', 'encoding'=>'string'],
 		'mb_str_split' => ['list<string>', 'str'=>'string', 'split_length='=>'positive-int', 'encoding='=>'string'],
 		'mb_strlen' => ['0|positive-int', 'str'=>'string', 'encoding='=>'string'],
diff --git a/tests/PHPStan/Analyser/nsrt/bug-8922-php74.php b/tests/PHPStan/Analyser/nsrt/bug-8922-php74.php
new file mode 100644
index 0000000000..1a0af68920
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-8922-php74.php
@@ -0,0 +1,19 @@
+<?php // lint < 8.0
+
+namespace Bug8922PHP74;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param non-empty-list<non-falsy-string> $array
+ * @param non-falsy-string $string
+ * @param mixed $mixed
+ */
+function doSomething($array, $string, $mixed): void
+{
+	assertType('list<non-falsy-string>', mb_detect_order());
+	assertType('bool', mb_detect_order(null));
+	assertType('bool', mb_detect_order($array));
+	assertType('bool', mb_detect_order($string));
+	assertType('bool', mb_detect_order($mixed));
+}
diff --git a/tests/PHPStan/Analyser/nsrt/bug-8922.php b/tests/PHPStan/Analyser/nsrt/bug-8922.php
new file mode 100644
index 0000000000..d7e39b5a14
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-8922.php
@@ -0,0 +1,19 @@
+<?php // lint >= 8.0
+
+namespace Bug8922;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param non-empty-list<non-falsy-string> $array
+ * @param non-falsy-string $string
+ * @param mixed $mixed
+ */
+function doSomething($array, $string, $mixed): void
+{
+	assertType('list<non-falsy-string>', mb_detect_order());
+	assertType('list<non-falsy-string>', mb_detect_order(null));
+	assertType('bool', mb_detect_order($array));
+	assertType('bool', mb_detect_order($string));
+	assertType('bool|list<non-falsy-string>', mb_detect_order($mixed));
+}
diff --git a/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php b/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
index 7d83fec5f9..0063dd35e6 100644
--- a/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
+++ b/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
@@ -2248,6 +2248,21 @@ public function testBug12954(): void
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-12954.php'], []);
 	}
 
+	public function testBug8922(): void
+	{
+		$errors = [];
+		if (PHP_VERSION_ID < 80000) {
+			$errors[] = [
+				'Parameter #1 $encoding_list of function mb_detect_order expects non-empty-list<non-falsy-string>|non-falsy-string, null given.',
+				15,
+				'• Type #1 from the union: null is not a list.
+• Type #1 from the union: null is empty.',
+			];
+		}
+
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-8922.php'], $errors);
+	}
+
 	public function testBug13065(): void
 	{
 		$errors = [];