[**Minimal reproduction**](https://gitlab.com/ramirez7/bug-repros/-/tree/09db5f857df0a8689003cba9048148e8d1678916/haskell.nix/2022/05/ghc9-iserv-1483) I ran into this x-compiling `cleff`, which uses TH. Seems related to #1450, which does make some changes to the handling of these system libs. I got things working by manually symlinking these dlls in the iserv wrapper: https://github.com/ramirez7/haskell.nix/blob/35c988ccdead5f66f7e11a41129cbf649445040c/overlays/mingw_w64.nix#L41-L45 This issue was only present in GHC 9 - everything worked fine with 8.10.7.