It looks like ghc in Debian unstable is defaulting to new style cabal builds which bypasses `Bootstrap.bootstrapWith Bootstrap.OSOnly`: ... git branch origin/spw3conf gpg signature verified; merging Already up to date. Build profile: -w ghc-8.8.3 -O1 In order, the following will be built (use -v for more details): - IfElse-0.85 (lib:IfElse) (requires build) - first-class-families-0.8.0.0 (lib) (requires build) - hsc2hs-0.68.7 (exe:hsc2hs) (requires download & build) - old-locale-1.0.0.7 (lib) (requires build) - syb-0.7.1 (lib) (requires build) - th-abstraction-0.3.2.0 (lib) (requires build) - network-bsd-2.8.1.0 (lib) (requires build) - type-errors-0.2.0.0 (lib) (requires build) - hslogger-1.3.1.0 (lib) (requires build) - propellor-5.10.1 (lib) (first run) - propellor-5.10.1 (exe:propellor-config) (first run) Downloading hsc2hs-0.68.7 Configuring IfElse-0.85... Preprocessing library for IfElse-0.85.. Building library for IfElse-0.85.. [1 of 1] Compiling Control.Monad.IfElse ( Control/Monad/IfElse.hs, dist/build/Control/Monad/IfElse.o ) Downloaded hsc2hs-0.68.7 ... I think the simplest fix is to replace `cabal build` with `cabal v1-build` in `Propellor.Bootstrap.buildCommand`? --spwhitton