diff --git a/pytorch_forecasting/metrics/base_metrics.py b/pytorch_forecasting/metrics/base_metrics.py
index 041d24044..d757be67b 100644
--- a/pytorch_forecasting/metrics/base_metrics.py
+++ b/pytorch_forecasting/metrics/base_metrics.py
@@ -822,6 +822,9 @@ def mask_losses(self, losses: torch.Tensor, lengths: torch.Tensor, reduction: st
         """
         if reduction is None:
             reduction = self.reduction
+
+        if isinstance(losses, list): losses = losses[0]
+
         if losses.ndim > 0:
             # mask loss
             mask = torch.arange(losses.size(1), device=losses.device).unsqueeze(0) >= lengths.unsqueeze(-1)