diff --git a/train.py b/train.py
index 3b6ff866..1ccfaead 100644
--- a/train.py
+++ b/train.py
@@ -108,6 +108,13 @@ def train(model, criterion, criterion_st, optimizer, optimizer_st, scheduler,
             speaker_ids.append(speaker_mapping[speaker_name])
         speaker_ids = torch.LongTensor(speaker_ids)
 
+        if len(speaker_mapping) > c.num_speakers:
+            raise ValueError("It seems there are at least {} speakers in "
+                             "your dataset, while 'num_speakers' is set to {}. "
+                             "Found the following speakers: {}".format(len(speaker_mapping),
+                                                                       c.num_speakers,
+                                                                       list(speaker_mapping)))
+
         # set stop targets view, we predict a single stop token per r frames prediction
         stop_targets = stop_targets.view(text_input.shape[0],
                                          stop_targets.size(1) // c.r, -1)