diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 4a91b287986..085ac1d8d73 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -577,7 +577,8 @@ namespace ts.server {
             return this.pendingProjectUpdates.has(project.getProjectName());
         }
 
-        private sendProjectsUpdatedInBackgroundEvent() {
+        /* @internal */
+        sendProjectsUpdatedInBackgroundEvent() {
             if (!this.eventHandler) {
                 return;
             }
diff --git a/src/server/project.ts b/src/server/project.ts
index 9d8b3a36dd4..a97fb9a9bf0 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -164,7 +164,7 @@ namespace ts.server {
             return hasOneOrMoreJsAndNoTsFiles(this);
         }
 
-        public static resolveModule(moduleName: string, initialDir: string, host: ServerHost, log: (message: string) => void): {} {
+        public static resolveModule(moduleName: string, initialDir: string, host: ServerHost, log: (message: string) => void): {} | undefined {
             const resolvedPath = normalizeSlashes(host.resolvePath(combinePaths(initialDir, "node_modules")));
             log(`Loading ${moduleName} from ${initialDir} (resolved to ${resolvedPath})`);
             const result = host.require(resolvedPath, moduleName);
@@ -1102,6 +1102,11 @@ namespace ts.server {
             }
         }
 
+        /** Starts a new check for diagnostics. Call this if some file has updated that would cause diagnostics to be changed. */
+        refreshDiagnostics() {
+            this.projectService.sendProjectsUpdatedInBackgroundEvent();
+        }
+
         private enableProxy(pluginModuleFactory: PluginModuleFactory, configEntry: PluginImport) {
             try {
                 if (typeof pluginModuleFactory !== "function") {
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index 5d1ef5e7a75..16277d93b0c 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -7748,7 +7748,7 @@ declare namespace ts.server {
         private readonly cancellationToken;
         isNonTsProject(): boolean;
         isJsOnlyProject(): boolean;
-        static resolveModule(moduleName: string, initialDir: string, host: ServerHost, log: (message: string) => void): {};
+        static resolveModule(moduleName: string, initialDir: string, host: ServerHost, log: (message: string) => void): {} | undefined;
         isKnownTypesPackageName(name: string): boolean;
         installPackage(options: InstallPackageOptions): Promise<ApplyCodeActionCommandResult>;
         private readonly typingsCache;
@@ -7829,6 +7829,8 @@ declare namespace ts.server {
         protected removeRoot(info: ScriptInfo): void;
         protected enableGlobalPlugins(): void;
         protected enablePlugin(pluginConfigEntry: PluginImport, searchPaths: string[]): void;
+        /** Starts a new check for diagnostics. Call this if some file has updated that would cause diagnostics to be changed. */
+        refreshDiagnostics(): void;
         private enableProxy;
     }
     /**
@@ -8081,7 +8083,6 @@ declare namespace ts.server {
         updateTypingsForProject(response: SetTypings | InvalidateCachedTypings | PackageInstalledResponse): void;
         private delayEnsureProjectForOpenFiles;
         private delayUpdateProjectGraph;
-        private sendProjectsUpdatedInBackgroundEvent;
         private delayUpdateProjectGraphs;
         setCompilerOptionsForInferredProjects(projectCompilerOptions: protocol.ExternalProjectCompilerOptions, projectRootPath?: string): void;
         findProject(projectName: string): Project | undefined;