When I run my program, I get a stack overflow message (current stacksize is 8388608 bytes) and the advice to use +RTS -Ksize -RTS The Haskell code creates a Windows dll, so no command line. That's why I want to change the stack size at compile time. I tried ghc -shared -O2 -o -with-rtsopts="-H128m -K64m" TBGlas.dll TBGlasDll.hs Ghc tells that it links with "-H128m -K64m". When I run the program I still get a message overflow with again the same (?) 8388608 stack size. I also changed the stacksize of the calling program, but no luck (same message). I wonder whether ghc ignores the -with-rtsopts parameter? Probably the problem is caused by not enough strictness, but still I want te make sure that it is not the stacksize (it is a big program). Kees