diff --git a/native_client/alphabet.cc b/native_client/alphabet.cc
index bd231a45..a2a00dc0 100644
--- a/native_client/alphabet.cc
+++ b/native_client/alphabet.cc
@@ -69,6 +69,21 @@ Alphabet::init(const char *config_file)
   return 0;
 }
 
+void
+Alphabet::InitFromLabels(const std::vector<std::string>& labels)
+{
+  space_label_ = -2;
+  size_ = labels.size();
+  for (int i = 0; i < size_; ++i) {
+    const std::string& label = labels[i];
+    if (label == " ") {
+      space_label_ = i;
+    }
+    label_to_str_[i] = label;
+    str_to_label_[label] = i;
+  }
+}
+
 std::string
 Alphabet::SerializeText()
 {
diff --git a/native_client/alphabet.h b/native_client/alphabet.h
index 3eb26790..ad75dfc1 100644
--- a/native_client/alphabet.h
+++ b/native_client/alphabet.h
@@ -19,6 +19,9 @@ public:
 
   virtual int init(const char *config_file);
 
+  // Initialize directly from sequence of labels.
+  void InitFromLabels(const std::vector<std::string>& labels);
+
   // Serialize alphabet into a binary buffer.
   std::string Serialize();
 
diff --git a/native_client/ctcdecode/__init__.py b/native_client/ctcdecode/__init__.py
index 93365c80..82cdd308 100644
--- a/native_client/ctcdecode/__init__.py
+++ b/native_client/ctcdecode/__init__.py
@@ -45,13 +45,17 @@ class Scorer(swigwrapper.Scorer):
 class Alphabet(swigwrapper.Alphabet):
     """Convenience wrapper for Alphabet which calls init in the constructor"""
 
-    def __init__(self, config_path):
+    def __init__(self, config_path=None):
         super(Alphabet, self).__init__()
-        err = self.init(config_path.encode("utf-8"))
-        if err != 0:
-            raise ValueError(
-                "Alphabet initialization failed with error code 0x{:X}".format(err)
-            )
+        if config_path:
+            err = self.init(config_path.encode("utf-8"))
+            if err != 0:
+                raise ValueError(
+                    "Alphabet initialization failed with error code 0x{:X}".format(err)
+                )
+
+    def InitFromLabels(self, data):
+        return super(Alphabet, self).InitFromLabels([c.encode("utf-8") for c in data])
 
     def CanEncodeSingle(self, input):
         """
diff --git a/training/coqui_stt_training/util/config.py b/training/coqui_stt_training/util/config.py
index f954ff0c..52619d35 100755
--- a/training/coqui_stt_training/util/config.py
+++ b/training/coqui_stt_training/util/config.py
@@ -11,11 +11,13 @@ from attrdict import AttrDict
 from coqpit import MISSING, Coqpit, check_argument
 from coqui_stt_ctcdecoder import Alphabet, UTF8Alphabet
 from xdg import BaseDirectory as xdg
+from tqdm import tqdm
 
 from .augmentations import NormalizeSampleRate, parse_augmentations
 from .gpu import get_available_gpus
 from .helpers import parse_file_size
 from .io import path_exists_remote
+from .sample_collections import samples_from_sources
 
 
 class _ConfigSingleton:
@@ -120,9 +122,12 @@ class _SttConfig(Coqpit):
 
         # If neither `--alphabet_config_path` nor `--bytes_output_mode` were specified,
         # look for alphabet file alongside loaded checkpoint.
-        checkpoint_alphabet_file = os.path.join(
+        loaded_checkpoint_alphabet_file = os.path.join(
             self.load_checkpoint_dir, "alphabet.txt"
         )
+        saved_checkpoint_alphabet_file = os.path.join(
+            self.save_checkpoint_dir, "alphabet.txt"
+        )
 
         if self.bytes_output_mode and self.alphabet_config_path:
             raise RuntimeError(
@@ -132,15 +137,42 @@ class _SttConfig(Coqpit):
             self.alphabet = UTF8Alphabet()
         elif self.alphabet_config_path:
             self.alphabet = Alphabet(os.path.abspath(self.alphabet_config_path))
-        elif os.path.exists(checkpoint_alphabet_file):
+        elif os.path.exists(loaded_checkpoint_alphabet_file):
             print(
                 "I --alphabet_config_path not specified, but found an alphabet file "
-                f"alongside specified checkpoint ({checkpoint_alphabet_file}).\n"
-                "I Will use this alphabet file for this run."
+                f"alongside specified checkpoint ({loaded_checkpoint_alphabet_file}). "
+                "Will use this alphabet file for this run."
             )
-            self.alphabet = Alphabet(checkpoint_alphabet_file)
+            self.alphabet = Alphabet(loaded_checkpoint_alphabet_file)
+        elif self.train_files and self.dev_files and self.test_files:
+            # Generate alphabet automatically from input dataset, but only if
+            # fully specified, to avoid confusion in case a missing set has extra
+            # characters.
+            print(
+                "I --alphabet_config_path not specified, but all input datasets are "
+                "present (--train_files, --dev_files, --test_files). An alphabet "
+                "will be generated automatically from the data and placed alongside "
+                f"the checkpoint ({saved_checkpoint_alphabet_file})."
+            )
+            characters = set()
+            for sample in tqdm(
+                samples_from_sources(
+                    self.train_files + self.dev_files + self.test_files
+                )
+            ):
+                characters |= set(sample.transcript)
+            characters = list(sorted(characters))
+            print(f"I Generated alphabet characters: {characters}.")
+            self.alphabet = Alphabet()
+            self.alphabet.InitFromLabels(characters)
         else:
-            raise RuntimeError("Missing --alphabet_config_path flag, can't continue")
+            raise RuntimeError(
+                "Missing --alphabet_config_path flag. Couldn't find an alphabet file\n"
+                "alongside checkpoint, and input datasets are not fully specified\n"
+                "(--train_files, --dev_files, --test_files), so can't generate an alphabet.\n"
+                "Either specify an alphabet file or fully specify the dataset, so one will\n"
+                "be generated automatically."
+            )
 
         # Geometric Constants
         # ===================