diff --git a/main.py b/main.py
index c6435d9..1776f4b 100644
--- a/main.py
+++ b/main.py
@@ -29,14 +29,16 @@ def running(local_rank, config, task, backup_config=False, setup_output_dir=Fals
     if setup_output_dir:
         output_dir = Path(config.result_dir) / config.name if config.output_dir is None else config.output_dir
         config.output_dir = str(output_dir)
-        if idist.get_rank() == 0:
-            if not output_dir.exists():
+        if output_dir.exists():
+            assert not any(output_dir.iterdir()), "output_dir must be empty"
+        else:
+            if idist.get_rank() == 0:
                 output_dir.mkdir(parents=True)
                 logger.info(f"mkdir -p {output_dir}")
-            logger.info(f"output path: {config.output_dir}")
-            if backup_config:
-                with open(output_dir / "config.yml", "w+") as f:
-                    print(config.pretty(), file=f)
+        logger.info(f"output path: {config.output_dir}")
+        if backup_config and idist.get_rank() == 0:
+            with open(output_dir / "config.yml", "w+") as f:
+                print(config.pretty(), file=f)
 
     OmegaConf.set_readonly(config, True)