diff --git a/src/wp-includes/plugin.php b/src/wp-includes/plugin.php
index 3725292dcc..6e9de6c3f4 100644
--- a/src/wp-includes/plugin.php
+++ b/src/wp-includes/plugin.php
@@ -470,6 +470,9 @@ function do_action( $tag, ...$arg ) {
 
 	if ( empty( $arg ) ) {
 		$arg[] = '';
+	} elseif ( is_array( $arg[0] ) && 1 === count( $arg[0] ) && isset( $arg[0][0] ) && is_object( $arg[0][0] ) ) {
+		// Backward compatibility for PHP4-style passing of `array( &$this )` as action `$arg`.
+		$arg[0] = $arg[0][0];
 	}
 
 	$wp_filter[ $tag ]->do_action( $arg );
diff --git a/tests/phpunit/tests/actions.php b/tests/phpunit/tests/actions.php
index d23e6a63b2..e83b6bfc15 100644
--- a/tests/phpunit/tests/actions.php
+++ b/tests/phpunit/tests/actions.php
@@ -153,6 +153,25 @@ class Tests_Actions extends WP_UnitTestCase {
 		$this->assertEquals( array( $val1, $val2 ), array_pop( $argsvar3 ) );
 	}
 
+	/**
+	 * Tests PHP 4 notation for calling actions while passing in an object by reference.
+	 *
+	 * @ticket 48312
+	 */
+	function test_action_args_with_php4_syntax() {
+		$a   = new MockAction();
+		$tag = __FUNCTION__;
+		$val = new stdClass;
+
+		add_action( $tag, array( &$a, 'action' ) );
+		// Ņall the action with PHP 4 notation for passing object by reference.
+		do_action( $tag, array( &$val ) );
+
+		$call_count = $a->get_call_count();
+		$argsvar    = $a->get_args();
+		$this->assertSame( array( $val ), array_pop( $argsvar ) );
+	}
+
 	function test_action_priority() {
 		$a   = new MockAction();
 		$tag = __FUNCTION__;