diff --git a/src/weathergen/model/engines.py b/src/weathergen/model/engines.py
index 72486da2f..5369e6c6d 100644
--- a/src/weathergen/model/engines.py
+++ b/src/weathergen/model/engines.py
@@ -111,9 +111,9 @@ def forward(self, batch, pe_embed):
 
         # if the assert is hit, max_number_tokens_local_per_cell in config needs to be increased
         max_tokens = self.cf.get("ae_local_max_tokens_per_cell", 64)
-        assert (
-            batch.tokens_lens.flatten(0, 2).sum(0).max() <= max_tokens
-        ), "max number of tokens per cell for positional encoding exceeded."
+        assert batch.tokens_lens.flatten(0, 2).sum(0).max() <= max_tokens, (
+            "max number of tokens per cell for positional encoding exceeded."
+        )
         " Increase ae_local_max_tokens_per_cell in config."
 
         if batch.tokens_lens.shape[2] == 1:
diff --git a/src/weathergen/train/loss_modules/loss_functions.py b/src/weathergen/train/loss_modules/loss_functions.py
index f9f173fcf..0d741bc28 100644
--- a/src/weathergen/train/loss_modules/loss_functions.py
+++ b/src/weathergen/train/loss_modules/loss_functions.py
@@ -62,9 +62,39 @@ def stats_normalized_erf(target, ens, mu, stddev):
     return torch.mean(d * d)  # + torch.mean( torch.sqrt( stddev) )
 
 
-def mse_ens(target, ens, mu, stddev):
-    mse_loss = torch.nn.functional.mse_loss
-    return torch.stack([mse_loss(target, mem) for mem in ens], 0).mean()
+def mse_ens(
+    target: torch.Tensor,
+    pred: torch.Tensor,
+    weights_channels: torch.Tensor | None,
+    weights_points: torch.Tensor | None,
+    use_ensemble_mean: bool = False,
+):
+    """
+    MSE loss for ensemble predictions, with two modes:
+
+    use_ensemble_mean=False (default):
+        Mean of per-member MSE — equivalent to mean(mse(target, mem) for mem in ens).
+        Penalises every member independently; each member is pushed toward the target.
+
+    use_ensemble_mean=True:
+        MSE of the ensemble mean against the target.
+        Collapses the ensemble to a single prediction before comparing, which
+        ignores spread and rewards a well-calibrated ensemble mean.
+
+    target : shape (num_data_points, num_channels)
+    pred   : shape (ens_dim, num_data_points, num_channels)
+    weights_channels : shape (num_channels,)  or None
+    weights_points   : shape (num_data_points,) or None
+    """
+    if use_ensemble_mean:
+        # lp_loss collapses the ensemble via .mean(0) before computing MSE
+        return mse(target, pred, weights_channels, weights_points)
+
+    losses, losses_chs = zip(
+        *[mse(target, member.unsqueeze(0), weights_channels, weights_points) for member in pred],
+        strict=False,
+    )
+    return torch.stack(list(losses)).mean(), torch.stack(list(losses_chs)).mean(0)
 
 
 def kernel_crps(