diff --git a/nets/loss.py b/nets/loss.py
index 43b54edc0cebcd5b101dbee6d4640a21491a2345..8de636c2224a21c6bd702069076017557df79d45 100644
--- a/nets/loss.py
+++ b/nets/loss.py
@@ -7,7 +7,7 @@ from nets.ious import box_ciou
 #   平滑标签
 #---------------------------------------------------#
 def _smooth_labels(y_true, label_smoothing):
-    num_classes = K.shape(y_true)[-1]
+    num_classes = tf.cast(K.shape(y_true)[-1], dtype=K.floatx())
     label_smoothing = K.constant(label_smoothing, dtype=K.floatx())
     return y_true * (1.0 - label_smoothing) + label_smoothing / num_classes
 #---------------------------------------------------#