diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index dcb9cce0adb..1b36d99d7c9 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -420,6 +420,7 @@ namespace ts {
             getTypeCount: () => getDiagnosticsProducingTypeChecker().getTypeCount(),
             getFileProcessingDiagnostics: () => fileProcessingDiagnostics,
             getResolvedTypeReferenceDirectives: () => resolvedTypeReferenceDirectives,
+            isSourceFileFromExternalLibrary,
             dropDiagnosticsProducingTypeChecker
         };
 
@@ -722,13 +723,17 @@ namespace ts {
                 getSourceFile: program.getSourceFile,
                 getSourceFileByPath: program.getSourceFileByPath,
                 getSourceFiles: program.getSourceFiles,
-                isSourceFileFromExternalLibrary: (file: SourceFile) => !!sourceFilesFoundSearchingNodeModules[file.path],
+                isSourceFileFromExternalLibrary,
                 writeFile: writeFileCallback || (
                     (fileName, data, writeByteOrderMark, onError, sourceFiles) => host.writeFile(fileName, data, writeByteOrderMark, onError, sourceFiles)),
                 isEmitBlocked,
             };
         }
 
+        function isSourceFileFromExternalLibrary(file: SourceFile): boolean {
+            return sourceFilesFoundSearchingNodeModules[file.path];
+        }
+
         function getDiagnosticsProducingTypeChecker() {
             return diagnosticsProducingTypeChecker || (diagnosticsProducingTypeChecker = createTypeChecker(program, /*produceDiagnostics:*/ true));
         }
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 9cf95d6de9b..a1e82a66595 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -17,7 +17,11 @@ namespace ts {
         readFile(path: string, encoding?: string): string;
         getFileSize?(path: string): number;
         writeFile(path: string, data: string, writeByteOrderMark?: boolean): void;
-        watchFile?(path: string, callback: FileWatcherCallback): FileWatcher;
+        /**
+         * @pollingInterval - this parameter is used in polling-based watchers and ignored in watchers that 
+         * use native OS file watching
+         */
+        watchFile?(path: string, callback: FileWatcherCallback, pollingInterval?: number): FileWatcher;
         watchDirectory?(path: string, callback: DirectoryWatcherCallback, recursive?: boolean): FileWatcher;
         resolvePath(path: string): string;
         fileExists(path: string): boolean;
@@ -449,7 +453,7 @@ namespace ts {
                 },
                 readFile,
                 writeFile,
-                watchFile: (fileName, callback) => {
+                watchFile: (fileName, callback, pollingInterval) => {
                     if (useNonPollingWatchers) {
                         const watchedFile = watchedFileSet.addFile(fileName, callback);
                         return {
@@ -457,7 +461,7 @@ namespace ts {
                         };
                     }
                     else {
-                        _fs.watchFile(fileName, { persistent: true, interval: 250 }, fileChanged);
+                        _fs.watchFile(fileName, { persistent: true, interval: pollingInterval || 250 }, fileChanged);
                         return {
                             close: () => _fs.unwatchFile(fileName, fileChanged)
                         };
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 37a3cc466a0..aa0b3e505f6 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2192,6 +2192,7 @@ namespace ts {
 
         /* @internal */ getFileProcessingDiagnostics(): DiagnosticCollection;
         /* @internal */ getResolvedTypeReferenceDirectives(): Map<ResolvedTypeReferenceDirective>;
+        /* @internal */ isSourceFileFromExternalLibrary(file: SourceFile): boolean;
         // For testing purposes only.
         /* @internal */ structureIsReused?: boolean;
     }
diff --git a/src/server/project.ts b/src/server/project.ts
index 563b0456910..d01df728248 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -301,7 +301,7 @@ namespace ts.server {
             return this.getLanguageService().getEmitOutput(info.fileName, emitOnlyDtsFiles);
         }
 
-        getFileNames() {
+        getFileNames(excludeFilesFromExternalLibraries?: boolean) {
             if (!this.program) {
                 return [];
             }
@@ -317,8 +317,14 @@ namespace ts.server {
                 }
                 return rootFiles;
             }
-            const sourceFiles = this.program.getSourceFiles();
-            return sourceFiles.map(sourceFile => asNormalizedPath(sourceFile.fileName));
+            const result: NormalizedPath[] = [];
+            for (const f of this.program.getSourceFiles()) {
+                if (excludeFilesFromExternalLibraries && this.program.isSourceFileFromExternalLibrary(f)) {
+                    continue;
+                }
+                result.push(asNormalizedPath(f.fileName));
+            }
+            return result;
         }
 
         getAllEmittableFiles() {
diff --git a/src/server/types.d.ts b/src/server/types.d.ts
index 95f9519cc38..aebc3121252 100644
--- a/src/server/types.d.ts
+++ b/src/server/types.d.ts
@@ -73,6 +73,6 @@ declare namespace ts.server {
     export interface InstallTypingHost extends JsTyping.TypingResolutionHost {
         writeFile(path: string, content: string): void;
         createDirectory(path: string): void;
-        watchFile?(path: string, callback: FileWatcherCallback): FileWatcher;
+        watchFile?(path: string, callback: FileWatcherCallback, pollingInterval?: number): FileWatcher;
     }
 }
\ No newline at end of file
diff --git a/src/server/typingsInstaller/typingsInstaller.ts b/src/server/typingsInstaller/typingsInstaller.ts
index a602a9f1a26..da97dbcd194 100644
--- a/src/server/typingsInstaller/typingsInstaller.ts
+++ b/src/server/typingsInstaller/typingsInstaller.ts
@@ -367,7 +367,7 @@ namespace ts.server.typingsInstaller {
                         this.sendResponse({ projectName: projectName, kind: server.ActionInvalidate });
                         isInvoked = true;
                     }
-                });
+                }, /*pollingInterval*/ 2000);
                 watchers.push(w);
             }
             this.projectWatchers[projectName] = watchers;
diff --git a/src/server/utilities.ts b/src/server/utilities.ts
index 9a832d22c8d..ac809652119 100644
--- a/src/server/utilities.ts
+++ b/src/server/utilities.ts
@@ -50,7 +50,7 @@ namespace ts.server {
     export function createInstallTypingsRequest(project: Project, typingOptions: TypingOptions, unresolvedImports: SortedReadonlyArray<string>, cachePath?: string): DiscoverTypings {
         return {
             projectName: project.getProjectName(),
-            fileNames: project.getFileNames(),
+            fileNames: project.getFileNames(/*excludeFilesFromExternalLibraries*/ true),
             compilerOptions: project.getCompilerOptions(),
             typingOptions,
             unresolvedImports,
diff --git a/src/services/jsTyping.ts b/src/services/jsTyping.ts
index 0f635c15174..316dcd355c2 100644
--- a/src/services/jsTyping.ts
+++ b/src/services/jsTyping.ts
@@ -88,7 +88,7 @@ namespace ts.JsTyping {
         exclude = typingOptions.exclude || [];
 
         const possibleSearchDirs = map(fileNames, getDirectoryPath);
-        if (projectRootPath !== undefined) {
+        if (projectRootPath) {
             possibleSearchDirs.push(projectRootPath);
         }
         searchDirs = deduplicate(possibleSearchDirs);