@mmaechler made some recent changes summarized e.g. at the [R-devel Daily NEWS feed for Dec 20](https://developer.r-project.org/blosxom.cgi/R-devel/2024/12/20#n2024-12-20) as > Enable defining ‘R_NO_REMAP_RMATH’ and calling ‘Rf_*()’ as has been documented in WRE for a while, fixing PR#18800 thanks to Mikael Jagan and Suharto Anggono. CRAN found sizeable side-effects (even more sizeable via recursive dependencies) from this for Rcpp. Specifically our file [sugar/undoRmath.h](https://github.com/RcppCore/Rcpp/blob/master/inst/include/Rcpp/sugar/undoRmath.h) needs conditional protection, and we have been in email exchange since. @kurthornik has already hot-patched two packages which are now up at CRAN, and I have been running reverse depends checks. A viable strategy appears to be to (for now) also condition the R-devel change on `defined(RCPP_SUGAR_UNDORMATH_H)` so that our header gets skipped, and add a version guard in the file. My pending changes also need check for `R_Version` being undefined (sigh...) but we check for that in one other place already. So a simple PR should be forthcoming. Needless to say, with nearly 3000 reverse dependencies just at CRAN we are hitting other issues. Two packages appear to have flattened namespace via `using`. In one example a call is made via a (global, not namespace protected) `Rf_runif()` (expecting a double in return) so this likely be `R::runif()` instead. We are trying to sort the corner cases out now, basic PR forthcoming once the reverse-depends run finishes in a few hours.