diff --git a/egs/librispeech/ASR/pruned_transducer_stateless4b/diagonalize.py b/egs/librispeech/ASR/pruned_transducer_stateless4b/diagonalize.py
index ec2bc9ceb..0aa0ef05a 100644
--- a/egs/librispeech/ASR/pruned_transducer_stateless4b/diagonalize.py
+++ b/egs/librispeech/ASR/pruned_transducer_stateless4b/diagonalize.py
@@ -259,5 +259,5 @@ class OrthogonalTransformation(nn.Module):
     @torch.no_grad()
     def get_transformation_out(self) -> Tensor:
         # see also get_transformation() above for notes on this.
-        cov = self.feats_cov
+        cov = 0.5 * (self.feats_cov + self.feats_cov.t())  # make sure symmetric
         return get_transformation(cov)