Appendix to “Amenable actions of real and p -adic algebraic groups” by Alain Valette

As a complement to Alain Valette’s article, this appendix gives an extension from group actions to groupoids of Proposition 2.4. Namely, it is shown that, for a smooth, second countable, locally compact groupoid endowed with a Borel Haar system, measurewise amenability is equivalent to amenability of the isotropy subgroups.