Fix issue #378

[HDembinski]

Fixes #378

[codecov]

Codecov Report

Merging #384 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           develop    #384   +/-   ##
=======================================
  Coverage     91.3%   91.3%           
=======================================
  Files           12      12           
  Lines          851     851           
=======================================
  Hits           777     777           
  Misses          74      74

Impacted Files	Coverage Δ
iminuit/_minuit_methods.py	94.89% <100%> (ø)	⬆️

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