diff --git a/ultralytics/utils/ops.py b/ultralytics/utils/ops.py
index 6dc6024a..34e6541a 100644
--- a/ultralytics/utils/ops.py
+++ b/ultralytics/utils/ops.py
@@ -215,7 +215,7 @@ def non_max_suppression(
 
     bs = prediction.shape[0]  # batch size
     nc = nc or (prediction.shape[1] - 4)  # number of classes
-    nm = prediction.shape[1] - nc - 4
+    nm = prediction.shape[1] - nc - 4  # number of masks
     mi = 4 + nc  # mask start index
     xc = prediction[:, 4:mi].amax(1) > conf_thres  # candidates