If you don’t know which new Samsung Galaxy phone to get for mobile virtual reality, one of the authorities on the subject has weighed in to make your decision easier.

For the best experience with the Gear VR head-mounted display peripheral, you should get the standard Galaxy S7 over the S7 Edge. At least, that’s the advice of Oculus VR chief technology officer John Carmack (via VRFocus). And the software engineer (best known for classic shooter Quake) would know. He’s in charge of the joint effort between Oculus and Samsung to design the Gear VR. And while the $599 Rift PC peripheral is the Facebook subsidiary’s top priority, it’s still putting a lot of work into ensuring the Gear VR is a great way for Galaxy owners to get into this new space at a relatively inexpensive $100 (on top of the cost of the smartphone). And that could help propel the VR sector to $30 billion in revenue by 2020 like tech advisor Digi-Capital is predicting.

Carmack explained his take on why the S7 Edge isn’t ideal for the Gear VR on Twitter yesterday following Samsung revealing all the details about the new devices. When a fan asked if the S7 or S7 Edge is best for Gear VR, Carmack didn’t hesitate to point out a few shortcomings with the Edge.

@hugotheonly1 @oculus the edge pixels aren't quite as well used, and it leaks a little more light — John Carmack (@ID_AA_Carmack) February 22, 2016

In the message, the Oculus CTO said Gear VR cannot fully use the S7 Edge’s pixels. On the standard S7, the screen is flat like on most other devices. But on the Edge, Samsung uses a a display that curves around the side of the handset. This creates a cool effect and enables Samsung to display more information, but it isn’t great for how the optics inside the Gear VR headset work.

Additionally, the Edge is bulkier, and Carmack says this causes more external light to leak into the Gear VR. That light can distract players, and it can even cause eye strain.

Now, none of this means the Edge is terrible for Gear VR. It’s probably still far better than sticking an iPhone into a Google Cardboard. All this means is that the one person who is in a position to know how to get the most from your Gear VR thinks the standard S7 is your best bet.