Rolling {1d20, 10}kh1 in a template

Can't quite figure out the syntax here.  I have the following feature on my Druid.

Starry Form

Dragon. When you make an INT or a WIS check, or a CONS saving throw to maintain concentration on a spell, you can treat a roll of 9 or lower on the d20 as a 10.

I've tried this

&{template:simple} {{charname=Quaf}} {{rname=Constitution Save}} {{mod=+2}} {{r1=[[{1d20,10}kh1 +2[CON]]]}} {{normal=1}}

But I get this error

Cannot mix sum and M rolls in a roll group

Any help on counting rolls under 9 as 10 within the template?

Seems like changing the 10 to 0d0+10 works

&{template:simple} {{charname=Quaf}} {{rname=Constitution Save}} {{mod=+2}} {{r1=[[{1d20,0d0+10}kh1 +2[CON]]] }} {{normal=1}}

David is correct. When you use a group like { }kh1, the values inside the { } must either be all dice rolls, or all numbers.

David's suggestion is a trick to change the 10 value so it looks like a dice roll to roll20, and so works properly.