diff --git a/egs/aishell/ASR/transducer_stateless/decoder.py b/egs/aishell/ASR/transducer_stateless/decoder.py
index dca084477..c2c6552a9 100644
--- a/egs/aishell/ASR/transducer_stateless/decoder.py
+++ b/egs/aishell/ASR/transducer_stateless/decoder.py
@@ -82,17 +82,17 @@ class Decoder(nn.Module):
         Returns:
           Return a tensor of shape (N, U, embedding_dim).
         """
-        embeding_out = self.embedding(y)
+        embedding_out = self.embedding(y)
         if self.context_size > 1:
-            embeding_out = embeding_out.permute(0, 2, 1)
+            embedding_out = embedding_out.permute(0, 2, 1)
             if need_pad is True:
-                embeding_out = F.pad(
-                    embeding_out, pad=(self.context_size - 1, 0)
+                embedding_out = F.pad(
+                    embedding_out, pad=(self.context_size - 1, 0)
                 )
             else:
                 # During inference time, there is no need to do extra padding
                 # as we only need one output
-                assert embeding_out.size(-1) == self.context_size
-            embeding_out = self.conv(embeding_out)
-            embeding_out = embeding_out.permute(0, 2, 1)
-        return embeding_out
+                assert embedding_out.size(-1) == self.context_size
+            embedding_out = self.conv(embedding_out)
+            embedding_out = embedding_out.permute(0, 2, 1)
+        return embedding_out
diff --git a/egs/aishell/ASR/transducer_stateless/export.py b/egs/aishell/ASR/transducer_stateless/export.py
index 641555bdb..5687260df 100755
--- a/egs/aishell/ASR/transducer_stateless/export.py
+++ b/egs/aishell/ASR/transducer_stateless/export.py
@@ -48,6 +48,7 @@ from pathlib import Path
 
 import sentencepiece as spm
 import torch
+import torch.nn as nn
 from conformer import Conformer
 from decoder import Decoder
 from joiner import Joiner
@@ -133,7 +134,7 @@ def get_params() -> AttributeDict:
     return params
 
 
-def get_encoder_model(params: AttributeDict):
+def get_encoder_model(params: AttributeDict) -> nn.Module:
     encoder = Conformer(
         num_features=params.feature_dim,
         output_dim=params.encoder_out_dim,
@@ -147,7 +148,7 @@ def get_encoder_model(params: AttributeDict):
     return encoder
 
 
-def get_decoder_model(params: AttributeDict):
+def get_decoder_model(params: AttributeDict) -> nn.Module:
     decoder = Decoder(
         vocab_size=params.vocab_size,
         embedding_dim=params.encoder_out_dim,
@@ -157,7 +158,7 @@ def get_decoder_model(params: AttributeDict):
     return decoder
 
 
-def get_joiner_model(params: AttributeDict):
+def get_joiner_model(params: AttributeDict) -> nn.Module:
     joiner = Joiner(
         input_dim=params.encoder_out_dim,
         output_dim=params.vocab_size,
@@ -165,7 +166,7 @@ def get_joiner_model(params: AttributeDict):
     return joiner
 
 
-def get_transducer_model(params: AttributeDict):
+def get_transducer_model(params: AttributeDict) -> nn.Module:
     encoder = get_encoder_model(params)
     decoder = get_decoder_model(params)
     joiner = get_joiner_model(params)
diff --git a/egs/aishell/ASR/transducer_stateless/pretrained.py b/egs/aishell/ASR/transducer_stateless/pretrained.py
index 65ac5f3ff..db89c4d67 100755
--- a/egs/aishell/ASR/transducer_stateless/pretrained.py
+++ b/egs/aishell/ASR/transducer_stateless/pretrained.py
@@ -44,11 +44,12 @@ Note: ./transducer_stateless/exp/pretrained.pt is generated by
 import argparse
 import logging
 import math
-from typing import List
 from pathlib import Path
+from typing import List
 
 import kaldifeat
 import torch
+import torch.nn as nn
 import torchaudio
 from beam_search import beam_search, greedy_search
 from conformer import Conformer
@@ -57,10 +58,10 @@ from joiner import Joiner
 from model import Transducer
 from torch.nn.utils.rnn import pad_sequence
 
-from icefall.env import get_env_info
-from icefall.utils import AttributeDict
-from icefall.lexicon import Lexicon
 from icefall.char_graph_compiler import CharCtcTrainingGraphCompiler
+from icefall.env import get_env_info
+from icefall.lexicon import Lexicon
+from icefall.utils import AttributeDict
 
 
 def get_parser():
@@ -150,7 +151,7 @@ def get_params() -> AttributeDict:
     return params
 
 
-def get_encoder_model(params: AttributeDict):
+def get_encoder_model(params: AttributeDict) -> nn.Module:
     encoder = Conformer(
         num_features=params.feature_dim,
         output_dim=params.encoder_out_dim,
@@ -164,7 +165,7 @@ def get_encoder_model(params: AttributeDict):
     return encoder
 
 
-def get_decoder_model(params: AttributeDict):
+def get_decoder_model(params: AttributeDict) -> nn.Module:
     decoder = Decoder(
         vocab_size=params.vocab_size,
         embedding_dim=params.encoder_out_dim,
@@ -174,7 +175,7 @@ def get_decoder_model(params: AttributeDict):
     return decoder
 
 
-def get_joiner_model(params: AttributeDict):
+def get_joiner_model(params: AttributeDict) -> nn.Module:
     joiner = Joiner(
         input_dim=params.encoder_out_dim,
         output_dim=params.vocab_size,
@@ -182,7 +183,7 @@ def get_joiner_model(params: AttributeDict):
     return joiner
 
 
-def get_transducer_model(params: AttributeDict):
+def get_transducer_model(params: AttributeDict) -> nn.Module:
     encoder = get_encoder_model(params)
     decoder = get_decoder_model(params)
     joiner = get_joiner_model(params)
diff --git a/egs/aishell/ASR/transducer_stateless/train.py b/egs/aishell/ASR/transducer_stateless/train.py
index 7da8e28a1..0c180b260 100755
--- a/egs/aishell/ASR/transducer_stateless/train.py
+++ b/egs/aishell/ASR/transducer_stateless/train.py
@@ -204,7 +204,7 @@ def get_params() -> AttributeDict:
     return params
 
 
-def get_encoder_model(params: AttributeDict):
+def get_encoder_model(params: AttributeDict) -> nn.Module:
     # TODO: We can add an option to switch between Conformer and Transformer
     encoder = Conformer(
         num_features=params.feature_dim,
@@ -219,7 +219,7 @@ def get_encoder_model(params: AttributeDict):
     return encoder
 
 
-def get_decoder_model(params: AttributeDict):
+def get_decoder_model(params: AttributeDict) -> nn.Module:
     decoder = Decoder(
         vocab_size=params.vocab_size,
         embedding_dim=params.encoder_out_dim,
@@ -229,7 +229,7 @@ def get_decoder_model(params: AttributeDict):
     return decoder
 
 
-def get_joiner_model(params: AttributeDict):
+def get_joiner_model(params: AttributeDict) -> nn.Module:
     joiner = Joiner(
         input_dim=params.encoder_out_dim,
         output_dim=params.vocab_size,
@@ -237,7 +237,7 @@ def get_joiner_model(params: AttributeDict):
     return joiner
 
 
-def get_transducer_model(params: AttributeDict):
+def get_transducer_model(params: AttributeDict) -> nn.Module:
     encoder = get_encoder_model(params)
     decoder = get_decoder_model(params)
     joiner = get_joiner_model(params)
diff --git a/egs/librispeech/ASR/conformer_ctc/train.py b/egs/librispeech/ASR/conformer_ctc/train.py
index c1fa814c0..cb0bd5c2d 100755
--- a/egs/librispeech/ASR/conformer_ctc/train.py
+++ b/egs/librispeech/ASR/conformer_ctc/train.py
@@ -41,6 +41,7 @@ from icefall.checkpoint import load_checkpoint
 from icefall.checkpoint import save_checkpoint as save_checkpoint_impl
 from icefall.dist import cleanup_dist, setup_dist
 from icefall.env import get_env_info
+from icefall.graph_compiler import CtcTrainingGraphCompiler
 from icefall.lexicon import Lexicon
 from icefall.utils import (
     AttributeDict,
@@ -123,6 +124,15 @@ def get_parser():
         """,
     )
 
+    parser.add_argument(
+        "--num-decoder-layers",
+        type=int,
+        default=6,
+        help="""Number of decoder layer of transformer decoder.
+        Setting this to 0 will not create the decoder at all (pure CTC model)
+        """,
+    )
+
     parser.add_argument(
         "--lr-factor",
         type=float,
@@ -210,7 +220,6 @@ def get_params() -> AttributeDict:
             "use_feat_batchnorm": True,
             "attention_dim": 512,
             "nhead": 8,
-            "num_decoder_layers": 6,
             # parameters for loss
             "beam_size": 10,
             "reduction": "sum",
@@ -357,9 +366,17 @@ def compute_loss(
         supervisions, subsampling_factor=params.subsampling_factor
     )
 
-    token_ids = graph_compiler.texts_to_ids(texts)
-
-    decoding_graph = graph_compiler.compile(token_ids)
+    if isinstance(graph_compiler, BpeCtcTrainingGraphCompiler):
+        # Works with a BPE model
+        token_ids = graph_compiler.texts_to_ids(texts)
+        decoding_graph = graph_compiler.compile(token_ids)
+    elif isinstance(graph_compiler, CtcTrainingGraphCompiler):
+        # Works with a phone lexicon
+        decoding_graph = graph_compiler.compile(texts)
+    else:
+        raise ValueError(
+            f"Unsupported type of graph compiler: {type(graph_compiler)}"
+        )
 
     dense_fsa_vec = k2.DenseFsaVec(
         nnet_output,
@@ -584,12 +601,38 @@ def run(rank, world_size, args):
     if torch.cuda.is_available():
         device = torch.device("cuda", rank)
 
-    graph_compiler = BpeCtcTrainingGraphCompiler(
-        params.lang_dir,
-        device=device,
-        sos_token="<sos/eos>",
-        eos_token="<sos/eos>",
-    )
+    if "lang_bpe" in params.lang_dir:
+        graph_compiler = BpeCtcTrainingGraphCompiler(
+            params.lang_dir,
+            device=device,
+            sos_token="<sos/eos>",
+            eos_token="<sos/eos>",
+        )
+    elif "lang_phone" in params.lang_dir:
+        assert params.att_rate == 0, (
+            "Attention decoder training does not support phone lang dirs "
+            "at this time due to a missing <sos/eos> symbol. Set --att-rate=0 "
+            "for pure CTC training when using a phone-based lang dir."
+        )
+        assert params.num_decoder_layers == 0, (
+            "Attention decoder training does not support phone lang dirs "
+            "at this time due to a missing <sos/eos> symbol. "
+            "Set --num-decoder-layers=0 for pure CTC training when using "
+            "a phone-based lang dir."
+        )
+        graph_compiler = CtcTrainingGraphCompiler(
+            lexicon,
+            device=device,
+        )
+        # Manually add the sos/eos ID with their default values
+        # from the BPE recipe which we're adapting here.
+        graph_compiler.sos_id = 1
+        graph_compiler.eos_id = 1
+    else:
+        raise ValueError(
+            f"Unsupported type of lang dir (we expected it to have "
+            f"'lang_bpe' or 'lang_phone' in its name): {params.lang_dir}"
+        )
 
     logging.info("About to create model")
     model = Conformer(
@@ -607,7 +650,9 @@ def run(rank, world_size, args):
 
     model.to(device)
     if world_size > 1:
-        model = DDP(model, device_ids=[rank])
+        # Note: find_unused_parameters=True is needed in case we
+        # want to set params.att_rate = 0 (i.e. att decoder is not trained)
+        model = DDP(model, device_ids=[rank], find_unused_parameters=True)
 
     optimizer = Noam(
         model.parameters(),
diff --git a/egs/librispeech/ASR/transducer/beam_search.py b/egs/librispeech/ASR/transducer/beam_search.py
index f45d06ce9..11032f31a 100644
--- a/egs/librispeech/ASR/transducer/beam_search.py
+++ b/egs/librispeech/ASR/transducer/beam_search.py
@@ -38,7 +38,9 @@ def greedy_search(model: Transducer, encoder_out: torch.Tensor) -> List[int]:
     blank_id = model.decoder.blank_id
     device = model.device
 
-    sos = torch.tensor([blank_id], device=device).reshape(1, 1)
+    sos = torch.tensor([blank_id], device=device, dtype=torch.int64).reshape(
+        1, 1
+    )
     decoder_out, (h, c) = model.decoder(sos)
     T = encoder_out.size(1)
     t = 0
diff --git a/egs/librispeech/ASR/transducer/model.py b/egs/librispeech/ASR/transducer/model.py
index fa0b2dd68..8305248c9 100644
--- a/egs/librispeech/ASR/transducer/model.py
+++ b/egs/librispeech/ASR/transducer/model.py
@@ -99,6 +99,7 @@ class Transducer(nn.Module):
         sos_y = add_sos(y, sos_id=blank_id)
 
         sos_y_padded = sos_y.pad(mode="constant", padding_value=blank_id)
+        sos_y_padded = sos_y_padded.to(torch.int64)
 
         decoder_out, _ = self.decoder(sos_y_padded)
 
diff --git a/egs/librispeech/ASR/transducer_lstm/beam_search.py b/egs/librispeech/ASR/transducer_lstm/beam_search.py
index dfc22fcf8..3531a9633 100644
--- a/egs/librispeech/ASR/transducer_lstm/beam_search.py
+++ b/egs/librispeech/ASR/transducer_lstm/beam_search.py
@@ -38,7 +38,9 @@ def greedy_search(model: Transducer, encoder_out: torch.Tensor) -> List[int]:
     blank_id = model.decoder.blank_id
     device = model.device
 
-    sos = torch.tensor([blank_id], device=device).reshape(1, 1)
+    sos = torch.tensor([blank_id], device=device, dtype=torch.int64).reshape(
+        1, 1
+    )
     decoder_out, (h, c) = model.decoder(sos)
     T = encoder_out.size(1)
     t = 0
diff --git a/egs/librispeech/ASR/transducer_lstm/model.py b/egs/librispeech/ASR/transducer_lstm/model.py
index cb9afd8a2..31843b60e 100644
--- a/egs/librispeech/ASR/transducer_lstm/model.py
+++ b/egs/librispeech/ASR/transducer_lstm/model.py
@@ -101,6 +101,7 @@ class Transducer(nn.Module):
         sos_y = add_sos(y, sos_id=sos_id)
 
         sos_y_padded = sos_y.pad(mode="constant", padding_value=blank_id)
+        sos_y_padded = sos_y_padded.to(torch.int64)
 
         decoder_out, _ = self.decoder(sos_y_padded)
 
diff --git a/egs/librispeech/ASR/transducer_stateless/beam_search.py b/egs/librispeech/ASR/transducer_stateless/beam_search.py
index 4f883092c..c5efb733d 100644
--- a/egs/librispeech/ASR/transducer_stateless/beam_search.py
+++ b/egs/librispeech/ASR/transducer_stateless/beam_search.py
@@ -47,7 +47,7 @@ def greedy_search(
     device = model.device
 
     decoder_input = torch.tensor(
-        [blank_id] * context_size, device=device
+        [blank_id] * context_size, device=device, dtype=torch.int64
     ).reshape(1, context_size)
 
     decoder_out = model.decoder(decoder_input, need_pad=False)
diff --git a/egs/librispeech/ASR/transducer_stateless/export.py b/egs/librispeech/ASR/transducer_stateless/export.py
index 641555bdb..5687260df 100755
--- a/egs/librispeech/ASR/transducer_stateless/export.py
+++ b/egs/librispeech/ASR/transducer_stateless/export.py
@@ -48,6 +48,7 @@ from pathlib import Path
 
 import sentencepiece as spm
 import torch
+import torch.nn as nn
 from conformer import Conformer
 from decoder import Decoder
 from joiner import Joiner
@@ -133,7 +134,7 @@ def get_params() -> AttributeDict:
     return params
 
 
-def get_encoder_model(params: AttributeDict):
+def get_encoder_model(params: AttributeDict) -> nn.Module:
     encoder = Conformer(
         num_features=params.feature_dim,
         output_dim=params.encoder_out_dim,
@@ -147,7 +148,7 @@ def get_encoder_model(params: AttributeDict):
     return encoder
 
 
-def get_decoder_model(params: AttributeDict):
+def get_decoder_model(params: AttributeDict) -> nn.Module:
     decoder = Decoder(
         vocab_size=params.vocab_size,
         embedding_dim=params.encoder_out_dim,
@@ -157,7 +158,7 @@ def get_decoder_model(params: AttributeDict):
     return decoder
 
 
-def get_joiner_model(params: AttributeDict):
+def get_joiner_model(params: AttributeDict) -> nn.Module:
     joiner = Joiner(
         input_dim=params.encoder_out_dim,
         output_dim=params.vocab_size,
@@ -165,7 +166,7 @@ def get_joiner_model(params: AttributeDict):
     return joiner
 
 
-def get_transducer_model(params: AttributeDict):
+def get_transducer_model(params: AttributeDict) -> nn.Module:
     encoder = get_encoder_model(params)
     decoder = get_decoder_model(params)
     joiner = get_joiner_model(params)
diff --git a/egs/librispeech/ASR/transducer_stateless/model.py b/egs/librispeech/ASR/transducer_stateless/model.py
index 76279a2eb..8281e1fb5 100644
--- a/egs/librispeech/ASR/transducer_stateless/model.py
+++ b/egs/librispeech/ASR/transducer_stateless/model.py
@@ -98,6 +98,7 @@ class Transducer(nn.Module):
         sos_y = add_sos(y, sos_id=blank_id)
 
         sos_y_padded = sos_y.pad(mode="constant", padding_value=blank_id)
+        sos_y_padded = sos_y_padded.to(torch.int64)
 
         decoder_out = self.decoder(sos_y_padded)
 
diff --git a/egs/librispeech/ASR/transducer_stateless/pretrained.py b/egs/librispeech/ASR/transducer_stateless/pretrained.py
index f2fb8d908..ad8d89918 100755
--- a/egs/librispeech/ASR/transducer_stateless/pretrained.py
+++ b/egs/librispeech/ASR/transducer_stateless/pretrained.py
@@ -59,6 +59,7 @@ from typing import List
 import kaldifeat
 import sentencepiece as spm
 import torch
+import torch.nn as nn
 import torchaudio
 from beam_search import beam_search, greedy_search, modified_beam_search
 from conformer import Conformer
@@ -159,7 +160,7 @@ def get_params() -> AttributeDict:
     return params
 
 
-def get_encoder_model(params: AttributeDict):
+def get_encoder_model(params: AttributeDict) -> nn.Module:
     encoder = Conformer(
         num_features=params.feature_dim,
         output_dim=params.encoder_out_dim,
@@ -173,7 +174,7 @@ def get_encoder_model(params: AttributeDict):
     return encoder
 
 
-def get_decoder_model(params: AttributeDict):
+def get_decoder_model(params: AttributeDict) -> nn.Module:
     decoder = Decoder(
         vocab_size=params.vocab_size,
         embedding_dim=params.encoder_out_dim,
@@ -183,7 +184,7 @@ def get_decoder_model(params: AttributeDict):
     return decoder
 
 
-def get_joiner_model(params: AttributeDict):
+def get_joiner_model(params: AttributeDict) -> nn.Module:
     joiner = Joiner(
         input_dim=params.encoder_out_dim,
         output_dim=params.vocab_size,
@@ -191,7 +192,7 @@ def get_joiner_model(params: AttributeDict):
     return joiner
 
 
-def get_transducer_model(params: AttributeDict):
+def get_transducer_model(params: AttributeDict) -> nn.Module:
     encoder = get_encoder_model(params)
     decoder = get_decoder_model(params)
     joiner = get_joiner_model(params)
diff --git a/egs/librispeech/ASR/transducer_stateless/train.py b/egs/librispeech/ASR/transducer_stateless/train.py
index 1accda09a..544f6e9b1 100755
--- a/egs/librispeech/ASR/transducer_stateless/train.py
+++ b/egs/librispeech/ASR/transducer_stateless/train.py
@@ -224,7 +224,7 @@ def get_params() -> AttributeDict:
     return params
 
 
-def get_encoder_model(params: AttributeDict):
+def get_encoder_model(params: AttributeDict) -> nn.Module:
     # TODO: We can add an option to switch between Conformer and Transformer
     encoder = Conformer(
         num_features=params.feature_dim,
@@ -239,7 +239,7 @@ def get_encoder_model(params: AttributeDict):
     return encoder
 
 
-def get_decoder_model(params: AttributeDict):
+def get_decoder_model(params: AttributeDict) -> nn.Module:
     decoder = Decoder(
         vocab_size=params.vocab_size,
         embedding_dim=params.encoder_out_dim,
@@ -249,7 +249,7 @@ def get_decoder_model(params: AttributeDict):
     return decoder
 
 
-def get_joiner_model(params: AttributeDict):
+def get_joiner_model(params: AttributeDict) -> nn.Module:
     joiner = Joiner(
         input_dim=params.encoder_out_dim,
         output_dim=params.vocab_size,
@@ -257,7 +257,7 @@ def get_joiner_model(params: AttributeDict):
     return joiner
 
 
-def get_transducer_model(params: AttributeDict):
+def get_transducer_model(params: AttributeDict) -> nn.Module:
     encoder = get_encoder_model(params)
     decoder = get_decoder_model(params)
     joiner = get_joiner_model(params)
diff --git a/icefall/graph_compiler.py b/icefall/graph_compiler.py
index b4c87d964..570ed7d7a 100644
--- a/icefall/graph_compiler.py
+++ b/icefall/graph_compiler.py
@@ -89,6 +89,29 @@ class CtcTrainingGraphCompiler(object):
 
         return decoding_graph
 
+    def texts_to_ids(self, texts: List[str]) -> List[List[int]]:
+        """Convert a list of texts to a list-of-list of word IDs.
+
+        Args:
+          texts:
+            It is a list of strings. Each string consists of space(s)
+            separated words. An example containing two strings is given below:
+
+                ['HELLO ICEFALL', 'HELLO k2']
+        Returns:
+          Return a list-of-list of word IDs.
+        """
+        word_ids_list = []
+        for text in texts:
+            word_ids = []
+            for word in text.split():
+                if word in self.word_table:
+                    word_ids.append(self.word_table[word])
+                else:
+                    word_ids.append(self.oov_id)
+            word_ids_list.append(word_ids)
+        return word_ids_list
+
     def convert_transcript_to_fsa(self, texts: List[str]) -> k2.Fsa:
         """Convert a list of transcript texts to an FsaVec.