diff --git a/src/vs/workbench/api/node/apiCommands.ts b/src/vs/workbench/api/node/apiCommands.ts
index 049f955bb8b..98eaf7888ca 100644
--- a/src/vs/workbench/api/node/apiCommands.ts
+++ b/src/vs/workbench/api/node/apiCommands.ts
@@ -49,7 +49,7 @@ export class OpenFolderAPICommand {
 			return executor.executeCommand('_files.pickFolderAndOpen', forceNewWindow);
 		}
 
-		return executor.executeCommand('_files.windowOpen', [uri.fsPath], forceNewWindow);
+		return executor.executeCommand('_files.windowOpen', [uri], forceNewWindow);
 	}
 }
 CommandsRegistry.registerCommand(OpenFolderAPICommand.ID, adjustHandler(OpenFolderAPICommand.execute));
diff --git a/src/vs/workbench/parts/files/electron-browser/fileCommands.ts b/src/vs/workbench/parts/files/electron-browser/fileCommands.ts
index 0d4a3cf8cc8..285ccefb058 100644
--- a/src/vs/workbench/parts/files/electron-browser/fileCommands.ts
+++ b/src/vs/workbench/parts/files/electron-browser/fileCommands.ts
@@ -79,9 +79,10 @@ export const ResourceSelectedForCompareContext = new RawContextKey<boolean>('res
 export const REMOVE_ROOT_FOLDER_COMMAND_ID = 'removeRootFolder';
 export const REMOVE_ROOT_FOLDER_LABEL = nls.localize('removeFolderFromWorkspace', "Remove Folder from Workspace");
 
-export const openWindowCommand = (accessor: ServicesAccessor, paths: string[], forceNewWindow: boolean) => {
+// support string paths for backward compatibility. TODO @bpasero remove if not necessary
+export const openWindowCommand = (accessor: ServicesAccessor, paths: (string | URI)[], forceNewWindow: boolean) => {
 	const windowService = accessor.get(IWindowService);
-	windowService.openWindow(paths.map(path => URI.file(path)), { forceNewWindow });
+	windowService.openWindow(paths.map(p => typeof p === 'string' ? URI.file(p) : p), { forceNewWindow });
 };
 
 function save(