IndexError in reduceArc

reduceArc FATAL: Failed on dataId={'visit': 41, 'dateObs': '2020-04-22', 'site': 'F', 'category': 'A', 'arm': 'r', 'spectrograph': 1, 'field': 'ARC', 'ccd': 1, 'filter': 'r', 'expTime': 5.0, 'dataType': 'ARC', 'taiObs': '2020-04-22', 'pfsDesignId': 1, 'slitOffset': 0.0}: IndexError: index 4553 is out of bounds for axis 0 with size 4176
Traceback (most recent call last):
  File "/scratch/pprice/jenkins/weekly/2020-05-11/build/stack/miniconda3-4.5.12-1172c30/Linux64/pipe_base/18.1.0/python/lsst/pipe/base/cmdLineTask.py", line 388, in __call__
    result = self.runTask(task, dataRef, kwargs)
  File "/scratch/pprice/jenkins/weekly/2020-05-11/build/stack/miniconda3-4.5.12-1172c30/Linux64/pipe_base/18.1.0/python/lsst/pipe/base/cmdLineTask.py", line 447, in runTask
    return task.runDataRef(dataRef, **kwargs)
  File "/scratch/pprice/jenkins/weekly/2020-05-11/build/stack/miniconda3-4.5.12-1172c30/Linux64/drp_stella/5.1.0-154-g1f188d6+1/python/pfs/drp/stella/reduceArcTask.py", line 191, in runDataRef
    self.identifyLines.run(spectra, detectorMap, lines)
  File "/scratch/pprice/jenkins/weekly/2020-05-11/build/stack/miniconda3-4.5.12-1172c30/Linux64/drp_stella/5.1.0-154-g1f188d6+1/python/pfs/drp/stella/identifyLines.py", line 49, in run
    self.identifyLines(spec, detectorMap, lines)
  File "/scratch/pprice/jenkins/weekly/2020-05-11/build/stack/miniconda3-4.5.12-1172c30/Linux64/drp_stella/5.1.0-154-g1f188d6+1/python/pfs/drp/stella/identifyLines.py", line 85, in identifyLines
    obsLines = sorted(obsLines, key=lambda xx: spectrum.spectrum[int(xx + 0.5)], reverse=True)
  File "/scratch/pprice/jenkins/weekly/2020-05-11/build/stack/miniconda3-4.5.12-1172c30/Linux64/drp_stella/5.1.0-154-g1f188d6+1/python/pfs/drp/stella/identifyLines.py", line 85, in <lambda>
    obsLines = sorted(obsLines, key=lambda xx: spectrum.spectrum[int(xx + 0.5)], reverse=True)
IndexError: index 4553 is out of bounds for axis 0 with size 4176