diff --git a/src/viewer/utils/utils_plot.py b/src/viewer/utils/utils_plot.py
index 174cadd..c519751 100644
--- a/src/viewer/utils/utils_plot.py
+++ b/src/viewer/utils/utils_plot.py
@@ -196,7 +196,7 @@ def on_hvar_change():
             key=f"plot_hvar_{plot_id}"
             sel_val=st.session_state[key]
             df_plots.loc[plot_id, "hvar"]=sel_val
-            df_plots.loc[plot_id, "hvals"]=[]
+            df_plots.at[plot_id, "hvals"]=[]
             
         hind = get_index_in_list(list_cols_ext, df_plots.loc[plot_id, "hvar"])
         st.selectbox(