diff --git a/mlair/plotting/postprocessing_plotting.py b/mlair/plotting/postprocessing_plotting.py
index 7fe6bc2fe82f50cb011f325707f102d51549c174..1cb6181ac5d1428012ce17a59b60da708085fe44 100644
--- a/mlair/plotting/postprocessing_plotting.py
+++ b/mlair/plotting/postprocessing_plotting.py
@@ -734,7 +734,8 @@ class PlotCompetitiveSkillScore(AbstractPlotClass):
         data = data.to_dataframe("data").unstack(level=1).swaplevel()
         data.columns = data.columns.levels[1]
         self._labels = [str(i) + "d" for i in data.index.levels[1].values]
-        return data.stack(level=0).reset_index(level=2, drop=True).reset_index(name="data")
+        data = data.stack(level=0).reset_index(level=2, drop=True).reset_index(name="data")
+        return data.astype({"comparison": str, "ahead": int, "data": float})
 
     def _plot(self, single_model_comparison=False):
         """Plot skill scores of the comparisons."""