https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95163
--- Comment #2 from John Donners <john.donners at atos dot net> --- hmm, indeed I found the applicable text in the standard (2.14) as well: "The effect of the firstprivate clause is as if it is applied to one or more constructs as follows: To the target construct if it is among the constituent constructs and the same list item does not appear in a lastprivate or map clause." Apologies for the invalid code. Splitting the two works without problems.
