diff --git a/stand/utils/dfh.py b/stand/utils/dfh.py
index 5cda416..a11e818 100644
--- a/stand/utils/dfh.py
+++ b/stand/utils/dfh.py
@@ -41,7 +41,7 @@ def dump_non_empty_df(df, fn, key="data"):
         print("<<< skip dumping empty dataframe")
         return
     print(f"<<< dump dataframe to {fn}")
-    df.to_hdf(fn, key)
+    df.to_hdf(fn, key=key)
     backup(df, fn, key) #TODO: test then remove