diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index 370c1a4cf22..ccd46004540 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -1470,7 +1470,7 @@ namespace ts.projectSystem {
             try {
                 projectService.openExternalProject({ projectFileName: "project", options: {}, rootFiles: toExternalFiles([file1.path, office.path]) });
                 const proj = projectService.externalProjects[0];
-                assert.deepEqual(proj.getFileNames(true), [file1.path]);
+                assert.deepEqual(proj.getFileNames(/*excludeFilesFromExternalLibraries*/ true), [file1.path]);
                 assert.deepEqual(proj.getTypeAcquisition().include, ["duck-types"]);
             } finally {
                 projectService.resetSafeList();