  The inverse transfer of magnetic helicity is investigated through direct
numerical simulations of large-scale-mechanically-driven turbulent flows in the
isothermal ideal magnetohydrodynamics (MHD) framework. The mechanical forcing
is either purely solenoidal or purely compressive and the turbulent
steady-states considered exhibit root mean square (RMS) Mach numbers 0.1
$\lesssim$ M $\lesssim$ 11. A continuous small-scale electromotive forcing
injects magnetic helical fluctuations, which lead to the build-up of ever
larger magnetic structures. Spectral scaling exponents are observed which, for
low Mach numbers, are consistent with previous research done in the
incompressible case. Higher compressibility leads to flatter magnetic helicity
scaling exponents. The deviations from the incompressible case are
comparatively small for solenoidally-driven turbulence, even at high Mach
numbers, as compared to those for compressively-driven turbulence, where strong
deviations are already visible at relatively mild RMS Mach numbers M $\gtrsim$
3. Compressible effects can thus play an important role in the inverse transfer
of magnetic helicity, especially when the turbulence drivers are rather
compressive. Theoretical results observed in the incompressible case can,
however, be transferred to supersonic turbulence by an appropriate change of
variables, using the Alfv\'en velocity in place of the magnetic field.
