diff --git a/src/vs/workbench/api/electron-browser/mainThreadWorkspace.ts b/src/vs/workbench/api/electron-browser/mainThreadWorkspace.ts
index 84d463aa91f..4d811d8df71 100644
--- a/src/vs/workbench/api/electron-browser/mainThreadWorkspace.ts
+++ b/src/vs/workbench/api/electron-browser/mainThreadWorkspace.ts
@@ -114,15 +114,15 @@ export class MainThreadWorkspace implements MainThreadWorkspaceShape {
 
 	// --- search ---
 
-	$startFileSearch(includePattern: string, includeFolder: string, excludePatternOrDisregardExcludes: string | false, maxResults: number, token: CancellationToken): Thenable<URI[]> {
+	$startFileSearch(includePattern: string, includeFolder: URI, excludePatternOrDisregardExcludes: string | false, maxResults: number, token: CancellationToken): Thenable<URI[]> {
 		const workspace = this._contextService.getWorkspace();
 		if (!workspace.folders.length) {
 			return undefined;
 		}
 
 		let folderQueries: IFolderQuery[];
-		if (typeof includeFolder === 'string') {
-			folderQueries = [{ folder: URI.file(includeFolder) }]; // if base provided, only search in that folder
+		if (includeFolder) {
+			folderQueries = [{ folder: includeFolder }]; // if base provided, only search in that folder
 		} else {
 			folderQueries = workspace.folders.map(folder => ({ folder: folder.uri })); // absolute pattern: search across all folders
 		}
diff --git a/src/vs/workbench/api/node/extHost.protocol.ts b/src/vs/workbench/api/node/extHost.protocol.ts
index 200aa028b52..46a8a5c7770 100644
--- a/src/vs/workbench/api/node/extHost.protocol.ts
+++ b/src/vs/workbench/api/node/extHost.protocol.ts
@@ -471,7 +471,7 @@ export interface ExtHostUrlsShape {
 }
 
 export interface MainThreadWorkspaceShape extends IDisposable {
-	$startFileSearch(includePattern: string, includeFolder: string, excludePatternOrDisregardExcludes: string | false, maxResults: number, token: CancellationToken): Thenable<UriComponents[]>;
+	$startFileSearch(includePattern: string, includeFolder: URI, excludePatternOrDisregardExcludes: string | false, maxResults: number, token: CancellationToken): Thenable<UriComponents[]>;
 	$startTextSearch(query: IPatternInfo, options: IQueryOptions, requestId: number, token: CancellationToken): Thenable<vscode.TextSearchComplete>;
 	$checkExists(includes: string[], token: CancellationToken): Thenable<boolean>;
 	$saveAll(includeUntitled?: boolean): Thenable<boolean>;
diff --git a/src/vs/workbench/api/node/extHostWorkspace.ts b/src/vs/workbench/api/node/extHostWorkspace.ts
index 9d23d2db985..50866d71b23 100644
--- a/src/vs/workbench/api/node/extHostWorkspace.ts
+++ b/src/vs/workbench/api/node/extHostWorkspace.ts
@@ -350,14 +350,15 @@ export class ExtHostWorkspace implements ExtHostWorkspaceShape {
 		this._logService.trace(`extHostWorkspace#findFiles: fileSearch, extension: ${extensionId}, entryPoint: findFiles`);
 
 		let includePattern: string;
-		let includeFolder: string;
+		let includeFolder: URI;
 		if (include) {
 			if (typeof include === 'string') {
 				includePattern = include;
 			} else {
 				includePattern = include.pattern;
-				includeFolder = include.base;
-				// TODO use include.baseFolder;
+
+				// include.base must be an absolute path
+				includeFolder = include.baseFolder || URI.file(include.base);
 			}
 		}