diff --git a/packages/python/plotly/plotly/express/_core.py b/packages/python/plotly/plotly/express/_core.py
index db8f002c2c1..404dd8012e9 100644
--- a/packages/python/plotly/plotly/express/_core.py
+++ b/packages/python/plotly/plotly/express/_core.py
@@ -928,6 +928,10 @@ def build_dataframe(args, attrables, array_attrables):
             length = len(df_output)
             if argument is None:
                 continue
+            # Ensure the field of "custom_data" is always list
+            if field == "custom_data":
+                if not isinstance(argument, list):
+                    argument = [argument]
             # Case of multiindex
             if isinstance(argument, pd.MultiIndex):
                 raise TypeError(