diff --git a/extensions/typescript-language-features/src/features/bufferSyncSupport.ts b/extensions/typescript-language-features/src/features/bufferSyncSupport.ts
index d63c8c3a81c..564325f563c 100644
--- a/extensions/typescript-language-features/src/features/bufferSyncSupport.ts
+++ b/extensions/typescript-language-features/src/features/bufferSyncSupport.ts
@@ -117,10 +117,16 @@ class SyncedBufferMap extends ResourceMap<SyncedBuffer> {
 }
 
 class PendingDiagnostics extends ResourceMap<number> {
-	public getFileList(): Set<string> {
-		return new Set(Array.from(this.entries)
-			.sort((a, b) => a[1] - b[1])
-			.map(entry => entry[0]));
+	public getOrderedFileSet(): ResourceMap<void> {
+		const orderedResources = Array.from(this.entries)
+			.sort((a, b) => a.value - b.value)
+			.map(entry => entry.resource);
+
+		const map = new ResourceMap<void>();
+		for (const resource of orderedResources) {
+			map.set(resource, void 0);
+		}
+		return map;
 	}
 }
 
@@ -128,7 +134,7 @@ class GetErrRequest {
 
 	public static executeGetErrRequest(
 		client: ITypeScriptServiceClient,
-		files: string[],
+		files: ResourceMap<void>,
 		onDone: () => void
 	) {
 		const token = new vscode.CancellationTokenSource();
@@ -139,13 +145,15 @@ class GetErrRequest {
 
 	private constructor(
 		client: ITypeScriptServiceClient,
-		public readonly files: string[],
+		public readonly files: ResourceMap<void>,
 		private readonly _token: vscode.CancellationTokenSource,
 		onDone: () => void
 	) {
 		const args: Proto.GeterrRequestArgs = {
 			delay: 0,
-			files
+			files: Array.from(files.entries)
+				.map(entry => client.normalizedPath(entry.resource))
+				.filter(x => !!x) as string[]
 		};
 
 		client.executeAsync('geterr', args, _token.token)
@@ -345,27 +353,25 @@ export default class BufferSyncSupport extends Disposable {
 	}
 
 	private sendPendingDiagnostics(): void {
-		const fileList = this.pendingDiagnostics.getFileList();
+		const orderedFileSet = this.pendingDiagnostics.getOrderedFileSet();
 
 		// Add all open TS buffers to the geterr request. They might be visible
 		for (const buffer of this.syncedBuffers.values) {
 			if (!this.pendingDiagnostics.has(buffer.resource)) {
-				fileList.add(buffer.filepath);
+				orderedFileSet.set(buffer.resource, void 0);
 			}
 		}
 
-		if (this.pendingGetErr) {
-			for (const file of this.pendingGetErr.files) {
-				fileList.add(file);
-			}
-		}
-
-		if (fileList.size) {
+		if (orderedFileSet.size) {
 			if (this.pendingGetErr) {
 				this.pendingGetErr.cancel();
+
+				for (const file of this.pendingGetErr.files.entries) {
+					orderedFileSet.set(file.resource, void 0);
+				}
 			}
 
-			const getErr = this.pendingGetErr = GetErrRequest.executeGetErrRequest(this.client, Array.from(fileList), () => {
+			const getErr = this.pendingGetErr = GetErrRequest.executeGetErrRequest(this.client, orderedFileSet, () => {
 				if (this.pendingGetErr === getErr) {
 					this.pendingGetErr = undefined;
 				}
diff --git a/extensions/typescript-language-features/src/utils/resourceMap.ts b/extensions/typescript-language-features/src/utils/resourceMap.ts
index 73364c03207..33d6f00b4be 100644
--- a/extensions/typescript-language-features/src/utils/resourceMap.ts
+++ b/extensions/typescript-language-features/src/utils/resourceMap.ts
@@ -15,12 +15,16 @@ import { getTempFile } from './temp';
  * file systems.
  */
 export class ResourceMap<T> {
-	private readonly _map = new Map<string, T>();
+	private readonly _map = new Map<string, { resource: vscode.Uri, value: T }>();
 
 	constructor(
-		private readonly _normalizePath?: (resource: vscode.Uri) => string | null
+		private readonly _normalizePath: (resource: vscode.Uri) => string | null = (resource) => resource.fsPath
 	) { }
 
+	public get size() {
+		return this._map.size;
+	}
+
 	public has(resource: vscode.Uri): boolean {
 		const file = this.toKey(resource);
 		return !!file && this._map.has(file);
@@ -28,13 +32,23 @@ export class ResourceMap<T> {
 
 	public get(resource: vscode.Uri): T | undefined {
 		const file = this.toKey(resource);
-		return file ? this._map.get(file) : undefined;
+		if (!file) {
+			return undefined;
+		}
+		const entry = this._map.get(file);
+		return entry ? entry.value : undefined;
 	}
 
 	public set(resource: vscode.Uri, value: T) {
 		const file = this.toKey(resource);
-		if (file) {
-			this._map.set(file, value);
+		if (!file) {
+			return;
+		}
+		const entry = this._map.get(file);
+		if (entry) {
+			entry.value = value;
+		} else {
+			this._map.set(file, { resource, value });
 		}
 	}
 
@@ -45,20 +59,20 @@ export class ResourceMap<T> {
 		}
 	}
 
-	public clear() {
+	public clear(): void {
 		this._map.clear();
 	}
 
 	public get values(): Iterable<T> {
+		return Array.from(this._map.values()).map(x => x.value);
+	}
+
+	public get entries(): Iterable<{ resource: vscode.Uri, value: T }> {
 		return this._map.values();
 	}
 
-	public get entries() {
-		return this._map.entries();
-	}
-
 	private toKey(resource: vscode.Uri): string | null {
-		const key = this._normalizePath ? this._normalizePath(resource) : resource.fsPath;
+		const key = this._normalizePath(resource);
 		if (!key) {
 			return key;
 		}