diff --git a/src/harness/unittests/session.ts b/src/harness/unittests/session.ts
index a505c3ee7be..74d1f5d0640 100644
--- a/src/harness/unittests/session.ts
+++ b/src/harness/unittests/session.ts
@@ -134,7 +134,7 @@ namespace ts.server {
                     type: "request",
                     arguments: {
                         formatOptions: {
-                            indentStyle: "Block"
+                            indentStyle: protocol.IndentStyle.Block,
                         }
                     }
                 };
@@ -149,11 +149,11 @@ namespace ts.server {
                     type: "request",
                     arguments: {
                         options: {
-                            module: "System",
-                            target: "ES5",
-                            jsx: "React",
-                            newLine: "Lf",
-                            moduleResolution: "Node"
+                            module: protocol.ModuleKind.System,
+                            target: protocol.ScriptTarget.ES5,
+                            jsx: protocol.JsxEmit.React,
+                            newLine: protocol.NewLineKind.Lf,
+                            moduleResolution: protocol.ModuleResolutionKind.Node,
                         }
                     }
                 };
diff --git a/src/server/protocol.ts b/src/server/protocol.ts
index c51743e1c39..d398555408b 100644
--- a/src/server/protocol.ts
+++ b/src/server/protocol.ts
@@ -2291,14 +2291,12 @@ namespace ts.server.protocol {
         body?: NavigationTree;
     }
 
-    export namespace IndentStyle {
-        export type None = "None";
-        export type Block = "Block";
-        export type Smart = "Smart";
+    export const enum IndentStyle {
+        None = "None",
+        Block = "Block",
+        Smart = "Smart",
     }
 
-    export type IndentStyle = IndentStyle.None | IndentStyle.Block | IndentStyle.Smart;
-
     export interface EditorSettings {
         baseIndentSize?: number;
         indentSize?: number;
@@ -2395,47 +2393,37 @@ namespace ts.server.protocol {
         [option: string]: CompilerOptionsValue | undefined;
     }
 
-    export namespace JsxEmit {
-        export type None = "None";
-        export type Preserve = "Preserve";
-        export type ReactNative = "ReactNative";
-        export type React = "React";
+    export const enum JsxEmit {
+        None = "None",
+        Preserve = "Preserve",
+        ReactNative = "ReactNative",
+        React = "React",
     }
 
-    export type JsxEmit = JsxEmit.None | JsxEmit.Preserve | JsxEmit.React | JsxEmit.ReactNative;
-
-    export namespace ModuleKind {
-        export type None = "None";
-        export type CommonJS = "CommonJS";
-        export type AMD = "AMD";
-        export type UMD = "UMD";
-        export type System = "System";
-        export type ES6 = "ES6";
-        export type ES2015 = "ES2015";
+    export const enum ModuleKind {
+        None = "None",
+        CommonJS = "CommonJS",
+        AMD = "AMD",
+        UMD = "UMD",
+        System = "System",
+        ES6 = "ES6",
+        ES2015 = "ES2015",
     }
 
-    export type ModuleKind = ModuleKind.None | ModuleKind.CommonJS | ModuleKind.AMD | ModuleKind.UMD | ModuleKind.System | ModuleKind.ES6 | ModuleKind.ES2015;
-
-    export namespace ModuleResolutionKind {
-        export type Classic = "Classic";
-        export type Node = "Node";
+    export const enum ModuleResolutionKind {
+        Classic = "Classic",
+        Node = "Node",
     }
 
-    export type ModuleResolutionKind = ModuleResolutionKind.Classic | ModuleResolutionKind.Node;
-
-    export namespace NewLineKind {
-        export type Crlf = "Crlf";
-        export type Lf = "Lf";
+    export const enum NewLineKind {
+        Crlf,
+        Lf,
     }
 
-    export type NewLineKind = NewLineKind.Crlf | NewLineKind.Lf;
-
-    export namespace ScriptTarget {
-        export type ES3 = "ES3";
-        export type ES5 = "ES5";
-        export type ES6 = "ES6";
-        export type ES2015 = "ES2015";
+    export const enum ScriptTarget {
+        ES3 = "ES3",
+        ES5 = "ES5",
+        ES6 = "ES6",
+        ES2015 = "ES2015",
     }
-
-    export type ScriptTarget = ScriptTarget.ES3 | ScriptTarget.ES5 | ScriptTarget.ES6 | ScriptTarget.ES2015;
 }