Oracle Corp. has altered its cloud licensing policy in a way that means anyone running its software on Amazon Web Services could be charged double what they were paying before.

News of the new policy comes by way of prominent Oracle blogger Tim Hall, who noted that under the previous licensing regime, AWS’s virtual central processing units were treated as a single thread of a core that runs two threads. This effectively meant that each virtual CPU was considered half a core for customer billing purposes.

But that’s no longer the case under Oracle’s updated cloud licensing policy, which now states that AWS virtual CPUs are treated as a full core unless hyperthreading is enabled. What this means is that customers using two AWS virtual CPUs now need to buy two Oracle licenses instead of just one, doubling their costs.

In addition, Oracle said that its Processor Core Factor Table, which states that Xeon cores count as just half a license, “is not applicable” any more. That would suggest customers would need to purchase twice as many licenses as before.

The Register, which first spotted Hall’s blog post, spoke to Pieter Jansen of the Oracle licensing consultancy Navicle Consulting, who confirmed that the analysis appears to be correct. He said that although the unit cost won’t change it does appear as if AWS cloud users will have to purchase twice as many Oracle licenses as they were using before. He added that the decision was likely to made to make Oracle’s own cloud seem like a more attractive option, and said it’s not clear yet if Oracle plans to make the new licensing conditions applicable to existing customers, or if they’ll be grandfathered into the new terms.

Oracle declined to comment on the reasons behind its licensing change.