diff --git a/egs/librispeech/ASR/conformer_ctc/pretrained.py b/egs/librispeech/ASR/conformer_ctc/pretrained.py
index 28724e1ebe..a2c0a54868 100755
--- a/egs/librispeech/ASR/conformer_ctc/pretrained.py
+++ b/egs/librispeech/ASR/conformer_ctc/pretrained.py
@@ -322,7 +322,7 @@ def main():
 
         H = k2.ctc_topo(
             max_token=max_token_id,
-            modified=False,
+            modified=params.num_classes > 500,
             device=device,
         )