diff --git a/src/Psalm/Internal/LanguageServer/LanguageServer.php b/src/Psalm/Internal/LanguageServer/LanguageServer.php
index 2b1dfafc7f6..c032d501cb7 100644
--- a/src/Psalm/Internal/LanguageServer/LanguageServer.php
+++ b/src/Psalm/Internal/LanguageServer/LanguageServer.php
@@ -15,6 +15,7 @@
 use Amp\Success;
 use Generator;
 use InvalidArgumentException;
+use JsonMapper;
 use LanguageServerProtocol\ClientCapabilities;
 use LanguageServerProtocol\CompletionOptions;
 use LanguageServerProtocol\Diagnostic;
@@ -108,6 +109,13 @@ class LanguageServer extends Dispatcher
      */
     protected $current_issues = [];
 
+    /**
+     * This should actually be a private property on `parent`
+     * @psalm-suppress UnusedProperty
+     * @var JsonMapper
+     */
+    protected $mapper;
+
     public function __construct(
         ProtocolReader $reader,
         ProtocolWriter $writer,