How to fix “set-mailbox : The value of property ‘ArchiveQuota’ must be greater than or equal to that of property ‘ArchiveWarningQuota'”

Trying to set a users mailbox to use the Database Quota Defaults…
set-mailbox -id testuser -UseDatabaseQuotaDefaults $false

…I stumbled upon the following error in Powershell:
set-mailbox : The value of property ‘ArchiveQuota’ must be greater than or equal to that of property ‘ArchiveWarningQuota’. ArchiveQuota: ‘100 GB (107,374,182,400 bytes)’, ArchiveWarningQuota: ‘966.8 GB (1,038,090,240,000 bytes)’.

Solving this issue is fairly easy. To reveal the problem, execute the following cmdlet (replace testuser for your own username)
get-mailbox testuser | fl *archive*

 … resulted in:
ArchiveQuota : 100 GB (107,374,182,400 bytes)
ArchiveWarningQuota : 966.8 GB (1,038,090,240,000 bytes)

So, to quickly solve the issue, downsize the ArchiveWarningQuota to a value below the ArchiveQuota:
set-Mailbox testuser -ArchiveWarningQuota 45GB