Error making alignments

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I am trying to make a dataset out of a small part of the LibriSpeech dataset to fine tune the Real-Time-Voice-Synthesis synthesizer for a single speaker. However, in order to fix an error I am trying data augmentation, adding a file to improve a particularly problematic word. When I try to call montrealforcedaligner I get

Traceback (most recent call last): File "aligner/command_line/align.py", line 186, in File "aligner/command_line/align.py", line 142, in validate_args File "aligner/command_line/align.py", line 85, in align_corpus File "aligner/corpus.py", line 543, in speaker_utterance_info ZeroDivisionError: division by zero.

All of the files were converted to wav before this operation btw.