diff --git a/src/Rules/Comparison/ImpossibleCheckTypeHelper.php b/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
index 0e5cc7c5e88..56052a105f8 100644
--- a/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
+++ b/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
@@ -308,6 +308,11 @@ private function findSpecifiedSureAndSureNotTypes(
 		return null;
 	}
 
+	/**
+	 * @param array<string|int, array{Expr, Type}> $sureOrSureNotTypes
+	 *
+	 * @return list<Type>
+	 */
 	private function sureUnionTypes(array $sureOrSureNotTypes, Expr $expr): array
 	{
 		$types = [];