diff --git a/gseapy/gsea.py b/gseapy/gsea.py
index a8c7673..1513a7a 100644
--- a/gseapy/gsea.py
+++ b/gseapy/gsea.py
@@ -101,7 +101,7 @@ def load_data(self, cls_vec: List[str]) -> Tuple[pd.DataFrame, Dict]:
             self._logger.warning(
                 "Found duplicated gene names, values averaged by gene names!"
             )
-            exprs = exprs.groupby(level=0).mean()
+            df = df.groupby(level=0).mean()
 
         # in case the description column is numeric
         if len(cls_vec) == (df.shape[1] - 1):