diff --git a/Userland/Libraries/LibCore/Forward.h b/Userland/Libraries/LibCore/Forward.h
index a279c8204c..c74b6b8797 100644
--- a/Userland/Libraries/LibCore/Forward.h
+++ b/Userland/Libraries/LibCore/Forward.h
@@ -34,6 +34,8 @@ class Object;
 class ObjectClassRegistration;
 class ProcessStatisticsReader;
 class Socket;
+template<typename Result>
+class Promise;
 class SocketAddress;
 class TCPServer;
 class TCPSocket;