diff --git a/utils/utils.py b/utils/utils.py
index 820bd936..d3a7ecf5 100755
--- a/utils/utils.py
+++ b/utils/utils.py
@@ -457,10 +457,10 @@ def build_targets(model, targets):
         t, a = targets, []
         gwh = t[:, 4:6] * ng
         if nt:
-            iou = wh_iou(anchor_vec, gwh)
+            iou = wh_iou(anchor_vec, gwh)  # iou(3,n) = wh_iou(anchor_vec(3,2), gwh(n,2))
 
             if use_all_anchors:
-                na = len(anchor_vec)  # number of anchors
+                na = anchor_vec.shape[0]  # number of anchors
                 a = torch.arange(na).view((-1, 1)).repeat([1, nt]).view(-1)
                 t = targets.repeat([na, 1])
                 gwh = gwh.repeat([na, 1])