I wrote a library called AmysGeometry. The only modules in it (so far) are: Amy/Geometry/ThreeD.hs Amy/Geometry/UnitSphere.hs The library compiles just fine, and I've been using it with other programs for a while. Then yesterday, I started getting the following error. Linking dist/build/add-centroids/add-centroids ... /usr/local/lib/AmysGeometry-1.0/ghc-7.0.3/libHSAmysGeometry-1.0.a(UnitSphere.o): In function `s3c6_info': (.text+0x4557): undefined reference to `__stginit_AmysGeometryzm1zi0_AmyziGeometry_' /usr/local/lib/AmysGeometry-1.0/ghc-7.0.3/libHSAmysGeometry-1.0.a(UnitSphere.o): (.data+0x3f0): undefined reference to `AmysGeometryzm1zi0_AmyziGeometry_DZCLocation_static_info' collect2: ld returned 1 exit status cabal: Error: some packages failed to install: I think this started because I recompiled some stuff with profiling. So I wiped out my current GHC and Haskell installation, re-installed it, and rebuilt AmysGeometry. But I'm still getting this error when I try to link with it. I would be grateful for any advice on how to diagnose this and fix it. Oh, and "ghc-pkg check" doesn't report any errors.