diff --git a/models.py b/models.py
index e93171f5..12c355b3 100755
--- a/models.py
+++ b/models.py
@@ -195,7 +195,7 @@ class YOLOLayer(nn.Module):
             io[..., :4] *= self.stride
 
             if 'default' in self.arc:  # seperate obj and cls
-                torch.sigmoid_(io[..., 4])
+                torch.sigmoid_(io[..., 4:])
             elif 'BCE' in self.arc:  # unified BCE (80 classes)
                 torch.sigmoid_(io[..., 5:])
                 io[..., 4] = 1
diff --git a/utils/utils.py b/utils/utils.py
index 74663bb2..0b81fcec 100755
--- a/utils/utils.py
+++ b/utils/utils.py
@@ -512,6 +512,8 @@ def non_max_suppression(prediction, conf_thres=0.5, iou_thres=0.5, multi_cls=Tru
     min_wh, max_wh = 2, 4096  # (pixels) minimum and maximum box width and height
 
     method = 'vision_batch'
+    nc = prediction[0].shape[1] - 5  # number of classes
+    multi_cls = multi_cls and (nc > 1)
     output = [None] * len(prediction)
     for image_i, pred in enumerate(prediction):
         # Apply conf constraint
@@ -525,7 +527,6 @@ def non_max_suppression(prediction, conf_thres=0.5, iou_thres=0.5, multi_cls=Tru
             continue
 
         # Compute conf
-        torch.sigmoid_(pred[..., 5:])
         pred[..., 5:] *= pred[..., 4:5]  # conf = obj_conf * cls_conf
 
         # Box (center x, center y, width, height) to (x1, y1, x2, y2)