diff --git a/CHANGELOG.md b/CHANGELOG.md
index b8968594f..9333033ba 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,10 @@ Note that Sockeye has checks in place to not translate with an old model that wa
 
 Each version section may have have subsections for: _Added_, _Changed_, _Removed_, _Deprecated_, and _Fixed_.
 
+## [1.18.54]
+### Added
+- `--source-factor-vocabs` can be set to provide source factor vocabularies.
+
 ## [1.18.53]
 ### Added
 - Always skipping softmax for greedy decoding by default, only for single models.
diff --git a/sockeye/__init__.py b/sockeye/__init__.py
index ded80be1e..81ba22787 100644
--- a/sockeye/__init__.py
+++ b/sockeye/__init__.py
@@ -11,4 +11,4 @@
 # express or implied. See the License for the specific language governing
 # permissions and limitations under the License.
 
-__version__ = '1.18.53'
+__version__ = '1.18.54'
diff --git a/sockeye/arguments.py b/sockeye/arguments.py
index 63ac61aa4..c457d7837 100644
--- a/sockeye/arguments.py
+++ b/sockeye/arguments.py
@@ -489,6 +489,12 @@ def add_vocab_args(params):
                         required=False,
                         default=None,
                         help='Existing target vocabulary (JSON).')
+    params.add_argument('--source-factor-vocabs',
+                        required=False,
+                        nargs='+',
+                        type=regular_file(),
+                        default=[],
+                        help='Existing source factor vocabulary (-ies) (JSON).')
     params.add_argument(C.VOCAB_ARG_SHARED_VOCAB,
                         action='store_true',
                         default=False,
diff --git a/sockeye/prepare_data.py b/sockeye/prepare_data.py
index 039b84b8a..e8f6a81d7 100644
--- a/sockeye/prepare_data.py
+++ b/sockeye/prepare_data.py
@@ -46,8 +46,8 @@ def prepare_data(args: argparse.Namespace):
     bucket_width = args.bucket_width
 
     source_paths = [args.source] + args.source_factors
-    # NOTE: Pre-existing source factor vocabularies not yet supported for prepare data
-    source_factor_vocab_paths = [None] * len(args.source_factors)
+    source_factor_vocab_paths = [args.source_factor_vocabs[i] if i < len(args.source_factor_vocabs)
+                                 else None for i in range(len(args.source_factors))]
     source_vocab_paths = [args.source_vocab] + source_factor_vocab_paths
 
     num_words_source, num_words_target = args.num_words
diff --git a/sockeye/train.py b/sockeye/train.py
index 4c7c06b80..49bd06d4d 100644
--- a/sockeye/train.py
+++ b/sockeye/train.py
@@ -301,7 +301,9 @@ def create_data_iters_and_vocabs(args: argparse.Namespace,
 
         else:
             # Load or create vocabs
-            source_vocab_paths = [args.source_vocab] + [None] * len(args.source_factors)
+            source_factor_vocab_paths = [args.source_factor_vocabs[i] if i < len(args.source_factor_vocabs)
+                                         else None for i in range(len(args.source_factors))]
+            source_vocab_paths = [args.source_vocab] + source_factor_vocab_paths
             target_vocab_path = args.target_vocab
             source_vocabs, target_vocab = vocab.load_or_create_vocabs(
                 source_paths=[args.source] + args.source_factors,
diff --git a/test/unit/test_arguments.py b/test/unit/test_arguments.py
index afaeb652d..f5fd212a8 100644
--- a/test/unit/test_arguments.py
+++ b/test/unit/test_arguments.py
@@ -35,8 +35,8 @@
           validation_source='test_validation_src', validation_target='test_validation_tgt',
           validation_source_factors=[],
           output='test_output', overwrite_output=False,
-          source_vocab=None, target_vocab=None, shared_vocab=False, num_words=(0, 0), word_min_count=(1, 1),
-          pad_vocab_to_multiple_of=None,
+          source_vocab=None, target_vocab=None, source_factor_vocabs=[], shared_vocab=False, num_words=(0, 0),
+          word_min_count=(1, 1), pad_vocab_to_multiple_of=None,
           no_bucketing=False, bucket_width=10, max_seq_len=(99, 99),
           monitor_pattern=None, monitor_stat_func='mx_default')),
 
@@ -50,8 +50,8 @@
           validation_source='test_validation_src', validation_target='test_validation_tgt',
           validation_source_factors=[],
           output='test_output', overwrite_output=False,
-          source_vocab=None, target_vocab=None, shared_vocab=False, num_words=(0, 0), word_min_count=(1, 1),
-          pad_vocab_to_multiple_of=None,
+          source_vocab=None, target_vocab=None, source_factor_vocabs=[], shared_vocab=False, num_words=(0, 0),
+          word_min_count=(1, 1), pad_vocab_to_multiple_of=None,
           no_bucketing=False, bucket_width=10, max_seq_len=(99, 99),
           monitor_pattern=None, monitor_stat_func='mx_default'))
 ])
@@ -337,6 +337,7 @@ def test_tutorial_averaging_args(test_params, expected_params, expected_params_p
           source_vocab=None,
           target_vocab=None,
           source_factors=[],
+          source_factor_vocabs=[],
           shared_vocab=False,
           num_words=(0, 0),
           word_min_count=(1, 1),
@@ -360,6 +361,7 @@ def test_tutorial_prepare_data_cli_args(test_params, expected_params):
           source_vocab=None,
           target_vocab=None,
           source_factors=[],
+          source_factor_vocabs=[],
           shared_vocab=False,
           num_words=(0, 0),
           word_min_count=(1, 1),