diff --git a/detection/validator/reward.py b/detection/validator/reward.py
index 6f5e870..4f5053b 100644
--- a/detection/validator/reward.py
+++ b/detection/validator/reward.py
@@ -36,11 +36,14 @@ def reward(y_pred: np.array, y_true: np.array) -> float:
     """
     preds = np.round(y_pred)
 
-    # accuracy = accuracy_score(y_true, preds)
-    cm = confusion_matrix(y_true, preds)
+    if len(y_true) == 0:
+        return 0, {'fp_score': 0, 'f1_score': 0, 'ap_score': 0}
+
+    # Handle single-class case where confusion_matrix returns 1x1
+    cm = confusion_matrix(y_true, preds, labels=[0, 1])
     tn, fp, fn, tp = cm.ravel()
-    f1 = f1_score(y_true, preds)
-    ap_score = average_precision_score(y_true, y_pred)
+    f1 = f1_score(y_true, preds, zero_division=0)
+    ap_score = average_precision_score(y_true, y_pred) if len(np.unique(y_true)) > 1 else 0.0
 
     res = {'fp_score': 1 - fp / len(y_pred),
            'f1_score': f1,