diff --git a/icefall/mmi.py b/icefall/mmi.py
index b7777b434..2de8f1aae 100644
--- a/icefall/mmi.py
+++ b/icefall/mmi.py
@@ -124,6 +124,7 @@ def _compute_mmi_loss_exact_non_optimized(
     den_tot_scores = den_lats.get_tot_scores(log_semiring=True, use_double_scores=True)
 
     tot_scores = num_tot_scores - den_scale * den_tot_scores
+    tot_scores = tot_scores.masked_fill(torch.isinf(tot_scores), 0.0)
 
     loss = -1 * tot_scores.sum()
     return loss