diff --git a/run-exp.py b/run-exp.py
index 56004ee2fc638da523e8c683af4f32582b542efc..c8b9453ab0e458f39e6fa117b4f4d5810f1e4278 100755
--- a/run-exp.py
+++ b/run-exp.py
@@ -41,7 +41,7 @@ class Variable:
 
         if var_type == "file":
             directory = pathlib.Path(value_config["directory"]).expanduser()
-            assert directory.exists() and directory.is_dir()
+            assert directory.exists() and directory.is_dir(), f"No such directory: {directory}"
 
             values = sorted(list(directory.iterdir()))