diff --git a/Zend/tests/bug71428.3.phpt b/Zend/tests/bug71428.3.phpt
new file mode 100644
index 00000000000..2f400e5952e
--- /dev/null
+++ b/Zend/tests/bug71428.3.phpt
@@ -0,0 +1,11 @@
+--TEST--
+bug #71428: Validation type inheritance with = NULL
+--FILE--
+<?php
+class A { }
+class B           {  public function m(A $a = NULL, $n) { echo "B.m";} };
+class C extends B {  public function m(A $a       , $n) { echo "C.m";} };
+?>
+--EXPECTF--
+Warning: Declaration of C::m(A $a, $n) should be compatible with B::m(A $a = NULL, $n) in %sbug71428.3.php on line 4
+
diff --git a/Zend/zend_inheritance.c b/Zend/zend_inheritance.c
index 5fd86c974f9..bb56b8e56f3 100644
--- a/Zend/zend_inheritance.c
+++ b/Zend/zend_inheritance.c
@@ -488,6 +488,8 @@ static ZEND_COLD zend_string *zend_get_function_declaration(const zend_function
 				} else {
 					smart_str_appends(&str, "NULL");
 				}
+			} else if (arg_info->type_hint && arg_info->allow_null) {
+				smart_str_appends(&str, " = NULL");
 			}
 
 			if (++i < num_args) {