diff --git a/egs/librispeech/ASR/conformer_ctc/checkpoint.py b/egs/librispeech/ASR/conformer_ctc/checkpoint.py
index f4a31f0b3..73d048605 100644
--- a/egs/librispeech/ASR/conformer_ctc/checkpoint.py
+++ b/egs/librispeech/ASR/conformer_ctc/checkpoint.py
@@ -1,3 +1,4 @@
+# copied from https://github.com/danpovey/quantization
 import torch
 from torch import nn
 from torch import Tensor
diff --git a/egs/librispeech/ASR/conformer_ctc/ckpnt_prediction.py b/egs/librispeech/ASR/conformer_ctc/ckpnt_prediction.py
index b0079d149..e745de687 100644
--- a/egs/librispeech/ASR/conformer_ctc/ckpnt_prediction.py
+++ b/egs/librispeech/ASR/conformer_ctc/ckpnt_prediction.py
@@ -1,3 +1,4 @@
+# copied from https://github.com/danpovey/quantization
 import torch
 from torch import nn
 from torch import Tensor
diff --git a/egs/librispeech/ASR/conformer_ctc/powerful_prediction.py b/egs/librispeech/ASR/conformer_ctc/powerful_prediction.py
index 142ccfdd6..7f5ae22ee 100644
--- a/egs/librispeech/ASR/conformer_ctc/powerful_prediction.py
+++ b/egs/librispeech/ASR/conformer_ctc/powerful_prediction.py
@@ -1,3 +1,4 @@
+# copied from https://github.com/danpovey/quantization
 import torch
 from torch import nn
 from torch import Tensor
diff --git a/egs/librispeech/ASR/conformer_ctc/prediction.py b/egs/librispeech/ASR/conformer_ctc/prediction.py
index e281f782d..edb201e91 100644
--- a/egs/librispeech/ASR/conformer_ctc/prediction.py
+++ b/egs/librispeech/ASR/conformer_ctc/prediction.py
@@ -1,3 +1,4 @@
+# copied from https://github.com/danpovey/quantization
 import torch
 from torch import nn
 from torch import Tensor
diff --git a/egs/librispeech/ASR/conformer_ctc/quantization.py b/egs/librispeech/ASR/conformer_ctc/quantization.py
index d865f0eb6..1bc3f7e8a 100644
--- a/egs/librispeech/ASR/conformer_ctc/quantization.py
+++ b/egs/librispeech/ASR/conformer_ctc/quantization.py
@@ -1,3 +1,4 @@
+# copied from https://github.com/danpovey/quantization
 import binascii
 import h5py
 import math