I found the issue. I called the symbol intptr_t in foreign.c and intptr in foreign.scm
Now both use intptr_t and uintptr_t, with patch below. Matt --- libguile/foreign.c-orig 2017-07-04 15:57:55.000000000 -0700 +++ libguile/foreign.c 2017-07-04 16:02:45.000000000 -0700 @@ -56,6 +56,8 @@ SCM_SYMBOL (sym_size_t, "size_t"); SCM_SYMBOL (sym_ssize_t, "ssize_t"); SCM_SYMBOL (sym_ptrdiff_t, "ptrdiff_t"); +SCM_SYMBOL (sym_intptr_t, "intptr_t"); +SCM_SYMBOL (sym_uintptr_t, "uintptr_t"); /* that's for pointers, you know. */ SCM_SYMBOL (sym_asterisk, "*"); @@ -1248,6 +1250,26 @@ #endif ); + scm_define (sym_intptr_t, +#if SCM_SIZEOF_INTPTR_T == 8 + scm_from_uint8 (SCM_FOREIGN_TYPE_INT64) +#elif SCM_SIZEOF_INTPTR_T == 4 + scm_from_uint8 (SCM_FOREIGN_TYPE_INT32) +#else +# error unsupported sizeof (scm_t_intptr) +#endif + ); + + scm_define (sym_uintptr_t, +#if SCM_SIZEOF_UINTPTR_T == 8 + scm_from_uint8 (SCM_FOREIGN_TYPE_UINT64) +#elif SCM_SIZEOF_UINTPTR_T == 4 + scm_from_uint8 (SCM_FOREIGN_TYPE_UINT32) +#else +# error unsupported sizeof (scm_t_uintptr) +#endif + ); + null_pointer = scm_cell (scm_tc7_pointer, 0); scm_define (sym_null, null_pointer); } --- module/system/foreign.scm-orig 2017-07-04 16:06:15.000000000 -0700 +++ module/system/foreign.scm 2017-07-04 16:44:27.000000000 -0700 @@ -30,6 +30,7 @@ uint16 int16 uint32 int32 uint64 int64 + intptr_t uintptr_t sizeof alignof