diff --git a/causalml/dataset/synthetic.py b/causalml/dataset/synthetic.py
index 983784fd..358ebb29 100644
--- a/causalml/dataset/synthetic.py
+++ b/causalml/dataset/synthetic.py
@@ -544,10 +544,10 @@ def scatter_plot_summary_holdout(
 
     for g in np.unique(group):
         ix = np.where(group == g)[0].tolist()
-        ax.scatter(xs[ix], ys[ix], c=cdict[g], label=g, s=100)
+        ax.scatter(xs.iloc[ix], ys.iloc[ix], c=cdict[g], label=g, s=100)
 
     for i, txt in enumerate(plot_data.label[:10]):
-        ax.annotate(txt, (xs[i] + 0.005, ys[i]))
+        ax.annotate(txt, (xs.iloc[i] + 0.005, ys.iloc[i]))
 
     ax.set_xlabel("Abs % Error of ATE")
     ax.set_ylabel("MSE")