I regret that I don't have a simpler failure case, but I'm just going to post this and please advise me. I don't see how to get debugging symbols to work to even look at a core dump. Usually I get a segfault, but sometimes I get this: _rsagl_modelview: internal error: evacuate: strange closure type 2053 (GHC version 6.10.1 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Aborted This program uses ffi, but in this checkin I've disabled RSAGL's ffi except the GLUT+OpenGL bindings. So it's OpenGL or ghc. The key to getting this error is the -G flag. -G4 or -G3 segfaults. Steps to replicate: git clone http://www.downstairspeople.org/git/rsagl.git cd rsagl/ git checkout possible_rts_bug_g4 cabal configure && cabal build ./dist/build/_rsagl_modelview/_rsagl_modelview +RTS -G4 -RTS <-- just sit and wait, it should display an animation briefly and then segfault. Friendly, --Lane