diff --git a/Userland/Libraries/LibCore/Forward.h b/Userland/Libraries/LibCore/Forward.h
index a0e81ec885..a279c8204c 100644
--- a/Userland/Libraries/LibCore/Forward.h
+++ b/Userland/Libraries/LibCore/Forward.h
@@ -25,6 +25,7 @@ class File;
 class IODevice;
 class LocalServer;
 class LocalSocket;
+class MappedFile;
 class MimeData;
 class NetworkJob;
 class NetworkResponse;