Fixes a parallel i/o issue

[sbryngelson]

Fixes #547, which only sometimes throws errors.

Checked on known non-working case (before/after). Also checked that things still work on known working compilers.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.83%. Comparing base (68a1b77) to head (ec22e0e).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #567      +/-   ##
==========================================
- Coverage   58.83%   58.83%   -0.01%     
==========================================
  Files          57       57              
  Lines       14559    14558       -1     
  Branches     1916     1916              
==========================================
- Hits         8566     8565       -1     
  Misses       5434     5434              
  Partials      559      559              

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