diff --git a/ext/spl/spl_iterators.c b/ext/spl/spl_iterators.c
index 731f7f7b6e866..4735a257a89e7 100644
--- a/ext/spl/spl_iterators.c
+++ b/ext/spl/spl_iterators.c
@@ -684,13 +684,17 @@ PHP_METHOD(RecursiveIteratorIterator, getDepth)
 PHP_METHOD(RecursiveIteratorIterator, getSubIterator)
 {
 	spl_recursive_it_object   *object = Z_SPLRECURSIVE_IT_P(ZEND_THIS);
-	zend_long  level = object->level;
+	zend_long level;
+	zend_bool level_is_null = 1;
 	zval *value;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "|l", &level) == FAILURE) {
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "|l!", &level, &level_is_null) == FAILURE) {
 		RETURN_THROWS();
 	}
-	if (level < 0 || level > object->level) {
+
+	if (level_is_null) {
+		level = object->level;
+	} else if (level < 0 || level > object->level) {
 		RETURN_NULL();
 	}
 
@@ -1318,14 +1322,14 @@ static spl_dual_it_object* spl_dual_it_construct(INTERNAL_FUNCTION_PARAMETERS, z
 		}
 		case DIT_IteratorIterator: {
 			zend_class_entry *ce_cast;
-			zend_string *class_name;
+			zend_string *class_name = NULL;
 
-			if (zend_parse_parameters(ZEND_NUM_ARGS(), "O|S", &zobject, ce_inner, &class_name) == FAILURE) {
+			if (zend_parse_parameters(ZEND_NUM_ARGS(), "O|S!", &zobject, ce_inner, &class_name) == FAILURE) {
 				return NULL;
 			}
 			ce = Z_OBJCE_P(zobject);
 			if (!instanceof_function(ce, zend_ce_iterator)) {
-				if (ZEND_NUM_ARGS() > 1) {
+				if (class_name) {
 					if (!(ce_cast = zend_lookup_class(class_name))
 					|| !instanceof_function(ce, ce_cast)
 					|| !ce_cast->get_iterator
diff --git a/ext/spl/spl_iterators.stub.php b/ext/spl/spl_iterators.stub.php
index ef2615d2ac8c4..4d99e60df451b 100644
--- a/ext/spl/spl_iterators.stub.php
+++ b/ext/spl/spl_iterators.stub.php
@@ -74,7 +74,7 @@ public function next() {}
     public function getDepth() {}
 
     /** @return RecursiveIterator|null */
-    public function getSubIterator(int $level = UNKNOWN) {}
+    public function getSubIterator(?int $level = null) {}
 
     /** @return RecursiveIterator */
     public function getInnerIterator() {}
@@ -115,8 +115,7 @@ public function getInnerIterator();
 
 class IteratorIterator implements OuterIterator
 {
-    /** @param Traversable $iterator */
-    public function __construct($iterator, string $class_name = UNKNOWN) {}
+    public function __construct(Traversable $iterator, ?string $class_name = null) {}
 
     /** @return Iterator|null */
     public function getInnerIterator() {}
diff --git a/ext/spl/spl_iterators_arginfo.h b/ext/spl/spl_iterators_arginfo.h
index f8d000e279aa1..7563521b46c84 100644
--- a/ext/spl/spl_iterators_arginfo.h
+++ b/ext/spl/spl_iterators_arginfo.h
@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 38fb46070ea48e774343e59de53797969acf4b06 */
+ * Stub hash: 65bcea1c2313ff50b3e15588e1cdba036995c131 */
 
 ZEND_BEGIN_ARG_INFO_EX(arginfo_class_EmptyIterator_current, 0, 0, 0)
 ZEND_END_ARG_INFO()
@@ -51,7 +51,7 @@ ZEND_END_ARG_INFO()
 #define arginfo_class_RecursiveIteratorIterator_getDepth arginfo_class_EmptyIterator_current
 
 ZEND_BEGIN_ARG_INFO_EX(arginfo_class_RecursiveIteratorIterator_getSubIterator, 0, 0, 0)
-	ZEND_ARG_TYPE_INFO(0, level, IS_LONG, 0)
+	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, level, IS_LONG, 1, "null")
 ZEND_END_ARG_INFO()
 
 #define arginfo_class_RecursiveIteratorIterator_getInnerIterator arginfo_class_EmptyIterator_current
@@ -79,8 +79,8 @@ ZEND_END_ARG_INFO()
 #define arginfo_class_OuterIterator_getInnerIterator arginfo_class_EmptyIterator_current
 
 ZEND_BEGIN_ARG_INFO_EX(arginfo_class_IteratorIterator___construct, 0, 0, 1)
-	ZEND_ARG_INFO(0, iterator)
-	ZEND_ARG_TYPE_INFO(0, class_name, IS_STRING, 0)
+	ZEND_ARG_OBJ_INFO(0, iterator, Traversable, 0)
+	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, class_name, IS_STRING, 1, "null")
 ZEND_END_ARG_INFO()
 
 #define arginfo_class_IteratorIterator_getInnerIterator arginfo_class_EmptyIterator_current