The -help output for -prune is aligned with the code.

In the code (.../src/init.cpp#L1063):
```
        if (nPruneTarget < MIN_DISK_SPACE_FOR_BLOCK_FILES) {
            return InitError(strprintf(_("Prune configured below the minimum of %d MiB.  Please use a higher number."), MIN_DISK_SPACE_FOR_BLOCK_FILES / 1024 / 1024));
        }
```
So correct value of nPruneTarget is **greater than or equal to** MIN_DISK_SPACE_FOR_BLOCK_FILES.

make check
./bitcoind --help