diff --git a/panda/src/express/virtualFileMountSystem.cxx b/panda/src/express/virtualFileMountSystem.cxx
index 5b3b510b1b..2ffe85b166 100644
--- a/panda/src/express/virtualFileMountSystem.cxx
+++ b/panda/src/express/virtualFileMountSystem.cxx
@@ -13,6 +13,7 @@
 ////////////////////////////////////////////////////////////////////
 
 #include "virtualFileMountSystem.h"
+#include "virtualFileSystem.h"
 
 TypeHandle VirtualFileMountSystem::_type_handle;