diff --git a/egs/wenetspeech/ASR/transducer_stateless/model.py b/egs/wenetspeech/ASR/transducer_stateless/model.py
index 9f9455bdd..9376fafdf 100644
--- a/egs/wenetspeech/ASR/transducer_stateless/model.py
+++ b/egs/wenetspeech/ASR/transducer_stateless/model.py
@@ -115,6 +115,7 @@ class Transducer(nn.Module):
         ]
         assert encoder_out.size(2) >= (max_sym_id + 1), [
             encoder_out.size(),
+            decoder_out.size(),
             max_sym_id,
         ]