diff --git a/pytorch_binding/warpctc_pytorch/__init__.py b/pytorch_binding/warpctc_pytorch/__init__.py
index b5bd390..081197b 100644
--- a/pytorch_binding/warpctc_pytorch/__init__.py
+++ b/pytorch_binding/warpctc_pytorch/__init__.py
@@ -42,7 +42,7 @@ def forward(ctx, acts, labels, act_lens, label_lens, size_average=False,
 
         if length_average:
             # Compute the avg. log-probability per batch sample and frame.
-            total_length = torch.prod(act_lens)
+            total_length = torch.sum(act_lens)
             grads = grads / total_length
             costs = costs / total_length
         elif size_average: