diff --git a/tests/fn.assertSignature.allNullable.phpt b/tests/fn.assertSignature.allNullable.phpt
index 139840883f904623d2eec7c77bacd2d321751045..4fadc005cad16a38104c8fb6142a4a710fafc7d6 100644
--- a/tests/fn.assertSignature.allNullable.phpt
+++ b/tests/fn.assertSignature.allNullable.phpt
@@ -11,6 +11,7 @@ $fn = function(?T1 $t1, ?T2 $t2): ?T3 {return new T3;};
 
 // Correct signature assertion
 assertSignature($fn, params(nullable(T1::class), nullable(T2::class)), nullable(T3::class));
+assertSignature($fn, params(nullable(T1::class), nullable(T2::class)), NULL); // no expectation about return type
 
 // parameter is nullable, non-nullable is expected
 Assert::exception(