diff --git a/egs/librispeech/ASR/zipformer/scaling.py b/egs/librispeech/ASR/zipformer/scaling.py
index e7c3f4ab1..60a348010 100644
--- a/egs/librispeech/ASR/zipformer/scaling.py
+++ b/egs/librispeech/ASR/zipformer/scaling.py
@@ -1032,7 +1032,7 @@ class WhiteningPenaltyFunction(torch.autograd.Function):
                         w.prob = w.max_prob
                         metric.backward()
                         penalty_grad = x_detached.grad
-                        scale = w.grad_scale * (
+                        scale = float(w.grad_scale) * (
                             x_grad.to(torch.float32).norm()
                             / (penalty_grad.norm() + 1.0e-20)
                         )
@@ -1074,7 +1074,7 @@ class Whiten(nn.Module):
         super(Whiten, self).__init__()
         assert num_groups >= 1
         assert float(whitening_limit) >= 1
-        assert grad_scale >= 0
+        assert float(grad_scale) >= 0
         self.num_groups = num_groups
         self.whitening_limit = whitening_limit
         self.grad_scale = grad_scale