Hello! I have a fairly long code here so I have yet to distill a short test case but I started to get a crash in 2.6.0 (I never saw this kind of error in earlier versions). Is there anything I can do to give you more helpful information besides the following error message? RPython traceback: File "pypy_module_pypyjit_interp_jit.c", line 149, in jump_absolute__AccessDirect_None File "rpython_jit_metainterp_warmstate.c", line 7443, in maybe_compile_and_run__star_5_1 File "rpython_jit_metainterp_warmstate.c", line 15882, in bound_reached__star_5_1 File "rpython_jit_metainterp_pyjitpl.c", line 7116, in compile_and_run_once___rpython_jit_metainterp_ji_5 File "rpython_jit_metainterp_pyjitpl.c", line 4903, in MetaInterp__compile_and_run_once File "rpython_jit_metainterp_pyjitpl.c", line 8771, in MetaInterp_interpret File "rpython_jit_metainterp_pyjitpl.c", line 13684, in MetaInterp__interpret File "rpython_jit_metainterp_pyjitpl.c", line 21400, in MIFrame_run_one_step File "rpython_jit_metainterp_pyjitpl_1.c", line 64946, in MIFrame_opimpl_jit_merge_point File "rpython_jit_metainterp_pyjitpl_2.c", line 50109, in MetaInterp_reached_loop_header File "rpython_jit_metainterp_pyjitpl_3.c", line 22634, in MetaInterp_compile_loop File "rpython_jit_metainterp_compile.c", line 12811, in compile_loop File "rpython_jit_metainterp_optimizeopt___init__.c", line 428, in optimize_trace File "rpython_jit_metainterp_optimizeopt_unroll.c", line 2607, in UnrollOptimizer_propagate_all_forward File "rpython_jit_metainterp_optimizeopt_unroll.c", line 21014, in UnrollOptimizer_close_loop File "rpython_jit_metainterp_optimizeopt_unroll.c", line 28710, in UnrollOptimizer_import_box File "rpython_jit_metainterp_optimizeopt_unroll.c", line 31670, in UnrollOptimizer_add_op_to_short ~~~ Crash in JIT! <KeyError object at 0x1017049c8> and `print sys.version`: 2.7.9 (295ee98b6928, May 31 2015, 07:28:49) [PyPy 2.6.0 with GCC 4.2.1 Compatible Apple LLVM 5.1 (clang-503.0.40)]