diff --git a/utils/utils.py b/utils/utils.py
index b961cbe6..7ef5a0c0 100755
--- a/utils/utils.py
+++ b/utils/utils.py
@@ -53,7 +53,7 @@ def labels_to_class_weights(labels):
     # Get class weights (inverse frequency) from training labels
     labels = np.concatenate(labels, 0)  # labels.shape = (866643, 5) for COCO
     classes = labels[:, 0].astype(np.int)
-    weights = 1 / (np.bincount(classes) + 1e-6)  # number of targets per class
+    weights = 1 / (np.bincount(classes, minlength=classes.max() + 1) + 1e-6)  # number of targets per class
     weights /= weights.sum()
     return torch.Tensor(weights)