diff --git a/extensions/gulp/src/main.ts b/extensions/gulp/src/main.ts
index 0314dc44fde41fd4fa7ff81a6a2386f8fe8fee3d..51a64054021460425505209c5117bc24d3885f52 100644
--- a/extensions/gulp/src/main.ts
+++ b/extensions/gulp/src/main.ts
@@ -68,7 +68,7 @@ interface GulpTaskDefinition extends vscode.TaskDefinition {
 
 class FolderDetector {
 
-	private fileWatcher: vscode.FileSystemWatcher;
+	private fileWatcher: vscode.FileSystemWatcher | undefined;
 	private promise: Thenable<vscode.Task[]> | undefined;
 
 	constructor(private _workspaceFolder: vscode.WorkspaceFolder) {