diff --git a/utils/utils.py b/utils/utils.py
index b724ccbd..5bc84fff 100755
--- a/utils/utils.py
+++ b/utils/utils.py
@@ -436,9 +436,10 @@ def compute_loss(p, targets, model):  # predictions, targets, model
     lcls *= h['cls']
     if red == 'sum':
         bs = tobj.shape[0]  # batch size
-        lbox *= 3 / ng
         lobj *= 3 / (6300 * bs) * 2  # 3 / np * 2
-        lcls *= 3 / ng / model.nc
+        if ng:
+            lcls *= 3 / ng / model.nc
+            lbox *= 3 / ng
 
     loss = lbox + lobj + lcls
     return loss, torch.cat((lbox, lobj, lcls, loss)).detach()