ghc-6.0.1 --make -O (linking errors)

Hi all, I recently switched to ghc 6.0.1 running on a debian linux box. When compiling a program using ghc --make -O or ghc --make -O2 I get lots of errors while linking. The linker concerns about undefined references to Data.FiniteMap, which I frequently use. For example, the linker says: ../Options.o(.text+0xc0d): In function `s4m5T_ret': : undefined reference to `DataziFiniteMap_lvl4_closure' Without optimizing my code, doing a plain ghc --make everything goes fine. Similarly, compiling the same program with the older ghc 6.0 I do not get any linking errors, whether I optimize or not. Any ideas, how I can get rid of the linking errors, except for switching back to ghc 6.0? Best Regards, Jan