diff --git a/.phan/config.php b/.phan/config.php
index 418f8e5bfb8..f46c9f6ad03 100644
--- a/.phan/config.php
+++ b/.phan/config.php
@@ -28,6 +28,7 @@ $cfg['minimum_target_php_version'] = '7.4.3';
 $cfg['file_list'] = array_merge(
 	$cfg['file_list'],
 	class_exists( Socket::class ) ? [] : [ '.phan/stubs/Socket.php' ],
+	class_exists( ReturnTypeWillChange::class ) ? [] : [ '.phan/stubs/ReturnTypeWillChange.php' ],
 	class_exists( AllowDynamicProperties::class ) ? [] : [ '.phan/stubs/AllowDynamicProperties.php' ],
 	[
 		// This makes constants and globals known to Phan before processing all other files.
diff --git a/.phan/stubs/ReturnTypeWillChange.php b/.phan/stubs/ReturnTypeWillChange.php
new file mode 100644
index 00000000000..d6da963ced3
--- /dev/null
+++ b/.phan/stubs/ReturnTypeWillChange.php
@@ -0,0 +1,6 @@
+<?php
+
+// Stub for PHP 8.1's ReturnTypeWillChange class
+#[Attribute]
+class ReturnTypeWillChange {
+}