diff --git a/Tests/Functional/lit.cfg b/Tests/Functional/lit.cfg
index 3d7799ca..78d6e1d9 100644
--- a/Tests/Functional/lit.cfg
+++ b/Tests/Functional/lit.cfg
@@ -119,6 +119,7 @@ else:
                 '-L', os.path.join(libdispatch_build_dir, 'src'),
                 '-L', os.path.join(libdispatch_build_dir, 'src', 'BlocksRuntime'),
                 '-L', os.path.join(libdispatch_build_dir, 'src', 'swift'),
+                '-vfsoverlay', os.path.join(libdispatch_build_dir, 'dispatch-vfs-overlay.yaml'),
             ])
 
             if platform.system() != 'Windows':