diff --git a/celltypist/classifier.py b/celltypist/classifier.py
index 2e353dc..1f43ada 100644
--- a/celltypist/classifier.py
+++ b/celltypist/classifier.py
@@ -468,7 +468,7 @@ def majority_vote(predictions: AnnotationResult, over_clustering: Union[list, tu
             over_clustering = np.array(over_clustering)
         logger.info("🗳️ Majority voting the predictions")
         votes = pd.crosstab(predictions.predicted_labels['predicted_labels'], over_clustering)
-        majority = votes.idxmax(axis=0)
+        majority = votes.idxmax(axis=0).astype(str)
         freqs = (votes / votes.sum(axis=0).values).max(axis=0)
         majority[freqs < min_prop] = 'Heterogeneous'
         majority = majority[over_clustering].reset_index()