diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 561419d367e..fad2db307aa 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -3,6 +3,7 @@
 /* @internal */
 namespace ts {
     export const emptyArray: never[] = [] as never[];
+    export const emptyMap: ReadonlyMap<never> = createMap<never>();
 
     export const externalHelpersModuleNameText = "tslib";
 
diff --git a/src/harness/unittests/typingsInstaller.ts b/src/harness/unittests/typingsInstaller.ts
index 5f6b1350578..a0a770ad093 100644
--- a/src/harness/unittests/typingsInstaller.ts
+++ b/src/harness/unittests/typingsInstaller.ts
@@ -1027,6 +1027,8 @@ namespace ts.projectSystem {
     });
 
     describe("discover typings", () => {
+        const emptySafeList = emptyMap;
+
         it("should use mappings from safe list", () => {
             const app = {
                 path: "/a/b/app.js",
@@ -1040,11 +1042,12 @@ namespace ts.projectSystem {
                 path: "/a/b/chroma.min.js",
                 content: ""
             };
-            const cache = createMap<string>();
+
+            const safeList = createMapFromTemplate({ jquery: "jquery", chroma: "chroma-js" });
 
             const host = createServerHost([app, jquery, chroma]);
             const logger = trackingLogger();
-            const result = JsTyping.discoverTypings(host, logger.log, [app.path, jquery.path, chroma.path], getDirectoryPath(<Path>app.path), /*safeListPath*/ undefined, cache, { enable: true }, []);
+            const result = JsTyping.discoverTypings(host, logger.log, [app.path, jquery.path, chroma.path], getDirectoryPath(<Path>app.path), safeList, emptyMap, { enable: true }, emptyArray);
             assert.deepEqual(logger.finish(), [
                 'Inferred typings from file names: ["jquery","chroma-js"]',
                 'Result: {"cachedTypingPaths":[],"newTypingNames":["jquery","chroma-js"],"filesToWatch":["/a/b/bower_components","/a/b/node_modules"]}',
@@ -1062,7 +1065,7 @@ namespace ts.projectSystem {
 
             for (const name of JsTyping.nodeCoreModuleList) {
                 const logger = trackingLogger();
-                const result = JsTyping.discoverTypings(host, logger.log, [f.path], getDirectoryPath(<Path>f.path), /*safeListPath*/ undefined, cache, { enable: true }, [name, "somename"]);
+                const result = JsTyping.discoverTypings(host, logger.log, [f.path], getDirectoryPath(<Path>f.path), emptySafeList, cache, { enable: true }, [name, "somename"]);
                 assert.deepEqual(logger.finish(), [
                     'Inferred typings from unresolved imports: ["node","somename"]',
                     'Result: {"cachedTypingPaths":[],"newTypingNames":["node","somename"],"filesToWatch":["/a/b/bower_components","/a/b/node_modules"]}',
@@ -1083,7 +1086,7 @@ namespace ts.projectSystem {
             const host = createServerHost([f, node]);
             const cache = createMapFromTemplate<string>({ "node": node.path });
             const logger = trackingLogger();
-            const result = JsTyping.discoverTypings(host, logger.log, [f.path], getDirectoryPath(<Path>f.path), /*safeListPath*/ undefined, cache, { enable: true }, ["fs", "bar"]);
+            const result = JsTyping.discoverTypings(host, logger.log, [f.path], getDirectoryPath(<Path>f.path), emptySafeList, cache, { enable: true }, ["fs", "bar"]);
             assert.deepEqual(logger.finish(), [
                 'Inferred typings from unresolved imports: ["node","bar"]',
                 'Result: {"cachedTypingPaths":["/a/b/node.d.ts"],"newTypingNames":["bar"],"filesToWatch":["/a/b/bower_components","/a/b/node_modules"]}',
@@ -1108,7 +1111,7 @@ namespace ts.projectSystem {
             const host = createServerHost([app, a, b]);
             const cache = createMap<string>();
             const logger = trackingLogger();
-            const result = JsTyping.discoverTypings(host, logger.log, [app.path], getDirectoryPath(<Path>app.path), /*safeListPath*/ undefined, cache, { enable: true }, /*unresolvedImports*/ []);
+            const result = JsTyping.discoverTypings(host, logger.log, [app.path], getDirectoryPath(<Path>app.path), emptySafeList, cache, { enable: true }, /*unresolvedImports*/ []);
             assert.deepEqual(logger.finish(), [
                 'Searching for typing names in /node_modules; all files: ["/node_modules/a/package.json"]',
                 'Result: {"cachedTypingPaths":[],"newTypingNames":["a"],"filesToWatch":["/bower_components","/node_modules"]}',
diff --git a/src/server/typingsInstaller/typingsInstaller.ts b/src/server/typingsInstaller/typingsInstaller.ts
index b1fddfb4129..8a3840fd984 100644
--- a/src/server/typingsInstaller/typingsInstaller.ts
+++ b/src/server/typingsInstaller/typingsInstaller.ts
@@ -85,6 +85,7 @@ namespace ts.server.typingsInstaller {
         private readonly missingTypingsSet: Map<true> = createMap<true>();
         private readonly knownCachesSet: Map<true> = createMap<true>();
         private readonly projectWatchers: Map<FileWatcher[]> = createMap<FileWatcher[]>();
+        private safeList: JsTyping.SafeList | undefined;
         readonly pendingRunRequests: PendingRequest[] = [];
 
         private installRunCount = 1;
@@ -143,12 +144,15 @@ namespace ts.server.typingsInstaller {
                 this.processCacheLocation(req.cachePath);
             }
 
+            if (this.safeList === undefined) {
+                this.safeList = JsTyping.loadSafeList(this.installTypingHost, this.safeListPath);
+            }
             const discoverTypingsResult = JsTyping.discoverTypings(
                 this.installTypingHost,
                 this.log.isEnabled() ? this.log.writeLine : undefined,
                 req.fileNames,
                 req.projectRootPath,
-                this.safeListPath,
+                this.safeList,
                 this.packageNameToTypingLocation,
                 req.typeAcquisition,
                 req.unresolvedImports);
diff --git a/src/services/jsTyping.ts b/src/services/jsTyping.ts
index 670633eb44b..84f2ef5ba9a 100644
--- a/src/services/jsTyping.ts
+++ b/src/services/jsTyping.ts
@@ -25,10 +25,6 @@ namespace ts.JsTyping {
         typings?: string;
     }
 
-    // A map of loose file names to library names
-    // that we are confident require typings
-    let safeList: Map<string>;
-
     /* @internal */
     export const nodeCoreModuleList: ReadonlyArray<string> = [
         "buffer", "querystring", "events", "http", "cluster",
@@ -40,6 +36,16 @@ namespace ts.JsTyping {
 
     const nodeCoreModules = arrayToMap(<string[]>nodeCoreModuleList, x => x);
 
+    /**
+     * A map of loose file names to library names that we are confident require typings
+     */
+    export type SafeList = ReadonlyMap<string>;
+
+    export function loadSafeList(host: TypingResolutionHost, safeListPath: Path): SafeList {
+        const result = readConfigFile(safeListPath, path => host.readFile(path));
+        return createMapFromTemplate<string>(result.config);
+    }
+
     /**
      * @param host is the object providing I/O related operations.
      * @param fileNames are the file names that belong to the same project
@@ -54,8 +60,8 @@ namespace ts.JsTyping {
         log: ((message: string) => void) | undefined,
         fileNames: string[],
         projectRootPath: Path,
-        safeListPath: Path,
-        packageNameToTypingLocation: Map<string>,
+        safeList: SafeList,
+        packageNameToTypingLocation: ReadonlyMap<string>,
         typeAcquisition: TypeAcquisition,
         unresolvedImports: ReadonlyArray<string>):
         { cachedTypingPaths: string[], newTypingNames: string[], filesToWatch: string[] } {
@@ -75,11 +81,6 @@ namespace ts.JsTyping {
             }
         });
 
-        if (!safeList) {
-            const result = readConfigFile(safeListPath, (path: string) => host.readFile(path));
-            safeList = createMapFromTemplate<string>(result.config);
-        }
-
         const filesToWatch: string[] = [];
 
         forEach(typeAcquisition.include, addInferredTyping);
diff --git a/src/services/shims.ts b/src/services/shims.ts
index e86e9053e57..b7c85d2ce82 100644
--- a/src/services/shims.ts
+++ b/src/services/shims.ts
@@ -1005,6 +1005,7 @@ namespace ts {
 
     class CoreServicesShimObject extends ShimBase implements CoreServicesShim {
         private logPerformance = false;
+        private safeList: JsTyping.SafeList | undefined;
 
         constructor(factory: ShimFactory, public readonly logger: Logger, private readonly host: CoreServicesShimHostAdapter) {
             super(factory);
@@ -1114,12 +1115,15 @@ namespace ts {
             const getCanonicalFileName = createGetCanonicalFileName(/*useCaseSensitivefileNames:*/ false);
             return this.forwardJSONCall("discoverTypings()", () => {
                 const info = <DiscoverTypingsInfo>JSON.parse(discoverTypingsJson);
-                return ts.JsTyping.discoverTypings(
+                if (this.safeList === undefined) {
+                    this.safeList = JsTyping.loadSafeList(this.host, toPath(info.safeListPath, info.safeListPath, getCanonicalFileName));
+                }
+                return JsTyping.discoverTypings(
                     this.host,
                     msg => this.logger.log(msg),
                     info.fileNames,
                     toPath(info.projectRootPath, info.projectRootPath, getCanonicalFileName),
-                    toPath(info.safeListPath, info.safeListPath, getCanonicalFileName),
+                    this.safeList,
                     info.packageNameToTypingLocation,
                     info.typeAcquisition,
                     info.unresolvedImports);