diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index 2f6ba7aa3bb..d098c91eecf 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -2028,7 +2028,7 @@ namespace ts.projectSystem {
             projectService.openExternalProject({ projectFileName, options: {}, rootFiles: [{ fileName: file1.path, scriptKind: ScriptKind.JS, hasMixedContent: true }] });
 
             checkNumberOfProjects(projectService, { externalProjects: 1 });
-            checkWatchedFiles(host, []);
+            checkWatchedFiles(host, [libFile.path]); // watching the "missing" lib file
 
             const project = projectService.externalProjects[0];
 
diff --git a/src/harness/unittests/typingsInstaller.ts b/src/harness/unittests/typingsInstaller.ts
index 9483308287f..6c43ea1c034 100644
--- a/src/harness/unittests/typingsInstaller.ts
+++ b/src/harness/unittests/typingsInstaller.ts
@@ -731,7 +731,7 @@ namespace ts.projectSystem {
             checkNumberOfProjects(projectService, { configuredProjects: 1 });
             const p = projectService.configuredProjects[0];
             checkProjectActualFiles(p, [app.path, jsconfig.path]);
-            checkWatchedFiles(host, [jsconfig.path, "/bower_components", "/node_modules"]);
+            checkWatchedFiles(host, [jsconfig.path, "/bower_components", "/node_modules", libFile.path]);
 
             installer.installAll(/*expectedCount*/ 1);
 
diff --git a/src/server/project.ts b/src/server/project.ts
index 18c203c194e..163510bad27 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -631,7 +631,7 @@ namespace ts.server {
                 // Missing files that are not yet watched should be added to the map.
                 missingFilePaths.forEach(p => {
                     if (!this.missingFilesMap.contains(p)) {
-                        const fileWatcher = ts.sys.watchFile(p, (_filename: string, removed?: boolean) => {
+                        const fileWatcher = this.projectService.host.watchFile(p, (_filename: string, removed?: boolean) => {
                             // removed = deleted ? true : (added ? false : undefined)
                             if (removed === false && this.missingFilesMap.contains(p)) {
                                 fileWatcher.close();