diff --git a/model_utils/model.py b/model_utils/model.py
index beb01fa94..5f51c6454 100644
--- a/model_utils/model.py
+++ b/model_utils/model.py
@@ -322,7 +322,15 @@ class DeepSpeech2Model(object):
         """
 
         def adapt_instance(instance):
-            padded_audio, text, audio_len = instance
+            if len(instance) < 2 or len(instance) > 3:
+                raise ValueError("Size of instance should be 2 or 3.")
+            padded_audio = instance[0]
+            text = instance[1]
+            # no padding part
+            if len(instance) == 2:
+                audio_len = padded_audio.shape[1]
+            else:
+                audio_len = instance[2]
             adapted_instance = [padded_audio, text]
             # Stride size for conv0 is (3, 2)
             # Stride size for conv1 to convN is (1, 2)