diff --git a/src/vs/workbench/api/common/extHostDiagnostics.ts b/src/vs/workbench/api/common/extHostDiagnostics.ts
index 499bbdbb28b..9097e5960ab 100644
--- a/src/vs/workbench/api/common/extHostDiagnostics.ts
+++ b/src/vs/workbench/api/common/extHostDiagnostics.ts
@@ -13,25 +13,20 @@ import * as converter from './extHostTypeConverters';
 import { mergeSort } from 'vs/base/common/arrays';
 import { Event, Emitter } from 'vs/base/common/event';
 import { ILogService } from 'vs/platform/log/common/log';
+import { ResourceMap } from 'vs/base/common/map';
 
 export class DiagnosticCollection implements vscode.DiagnosticCollection {
 
-	private readonly _name: string;
-	private readonly _owner: string;
-	private readonly _maxDiagnosticsPerFile: number;
-	private readonly _onDidChangeDiagnostics: Emitter<(vscode.Uri | string)[]>;
-	private readonly _proxy: MainThreadDiagnosticsShape | undefined;
-
 	private _isDisposed = false;
-	private _data = new Map<string, vscode.Diagnostic[]>();
+	private _data = new ResourceMap<vscode.Diagnostic[]>();
 
-	constructor(name: string, owner: string, maxDiagnosticsPerFile: number, proxy: MainThreadDiagnosticsShape | undefined, onDidChangeDiagnostics: Emitter<(vscode.Uri | string)[]>) {
-		this._name = name;
-		this._owner = owner;
-		this._maxDiagnosticsPerFile = maxDiagnosticsPerFile;
-		this._proxy = proxy;
-		this._onDidChangeDiagnostics = onDidChangeDiagnostics;
-	}
+	constructor(
+		private readonly _name: string,
+		private readonly _owner: string,
+		private readonly _maxDiagnosticsPerFile: number,
+		private readonly _proxy: MainThreadDiagnosticsShape | undefined,
+		private readonly _onDidChangeDiagnostics: Emitter<(vscode.Uri | string)[]>
+	) { }
 
 	dispose(): void {
 		if (!this._isDisposed) {
@@ -73,7 +68,7 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 			}
 
 			// update single row
-			this._data.set(first.toString(), diagnostics.slice());
+			this._data.set(first, diagnostics.slice());
 			toSync = [first];
 
 		} else if (Array.isArray(first)) {
@@ -87,8 +82,8 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 			for (const tuple of first) {
 				const [uri, diagnostics] = tuple;
 				if (!lastUri || uri.toString() !== lastUri.toString()) {
-					if (lastUri && this._data.get(lastUri.toString())!.length === 0) {
-						this._data.delete(lastUri.toString());
+					if (lastUri && this._data.get(lastUri)!.length === 0) {
+						this._data.delete(lastUri);
 					}
 					lastUri = uri;
 					toSync.push(uri);
@@ -120,7 +115,7 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 		const entries: [URI, IMarkerData[]][] = [];
 		for (let uri of toSync) {
 			let marker: IMarkerData[] = [];
-			const diagnostics = this._data.get(uri.toString());
+			const diagnostics = this._data.get(uri);
 			if (diagnostics) {
 
 				// no more than N diagnostics per file
@@ -160,7 +155,7 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 	delete(uri: vscode.Uri): void {
 		this._checkDisposed();
 		this._onDidChangeDiagnostics.fire([uri]);
-		this._data.delete(uri.toString());
+		this._data.delete(uri);
 		if (this._proxy) {
 			this._proxy.$changeMany(this._owner, [[uri, undefined]]);
 		}
@@ -177,15 +172,14 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 
 	forEach(callback: (uri: URI, diagnostics: ReadonlyArray<vscode.Diagnostic>, collection: DiagnosticCollection) => any, thisArg?: any): void {
 		this._checkDisposed();
-		this._data.forEach((value, key) => {
-			const uri = URI.parse(key);
+		this._data.forEach((value, uri) => {
 			callback.apply(thisArg, [uri, this.get(uri), this]);
 		});
 	}
 
 	get(uri: URI): ReadonlyArray<vscode.Diagnostic> {
 		this._checkDisposed();
-		const result = this._data.get(uri.toString());
+		const result = this._data.get(uri);
 		if (Array.isArray(result)) {
 			return <ReadonlyArray<vscode.Diagnostic>>Object.freeze(result.slice(0));
 		}
@@ -194,7 +188,7 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 
 	has(uri: URI): boolean {
 		this._checkDisposed();
-		return Array.isArray(this._data.get(uri.toString()));
+		return Array.isArray(this._data.get(uri));
 	}
 
 	private _checkDisposed() {