Here's an easy coredump: x = numpy.arange(10, dtype="f"); y = numpy.array(len(x), dtype="F"); y.imag += x Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000000 PyArray_CompareLists (l1=0x0, l2=0x1841618, n=1) at numpy/core/src/ multiarraymodule.c:132 132 if (l1[i] != l2[i]) return 0; (gdb) where #0 PyArray_CompareLists (l1=0x0, l2=0x1841618, n=1) at numpy/core/ src/multiarraymodule.c:132 #1 0x02a377d8 in PyUFunc_GenericFunction (self=0x538d40, args=0x2db3c88, mps=0xbfffd9c8) at numpy/core/src/ufuncobject.c:968 #2 0x02a39210 in ufunc_generic_call (self=0x538d40, args=0x2db3c88) at numpy/core/src/ufuncobject.c:2635 #3 0x000243bc in PyObject_CallFunction (callable=0x538d40, format=0x0) at Objects/abstract.c:1756 #4 0x0001f8cc in PyNumber_InPlaceAdd (v=0x565800, w=0x572540) at Objects/abstract.c:740 R