diff --git a/ports/zephyr/mpconfigport.h b/ports/zephyr/mpconfigport.h
index bf85ef6eaa..576618e368 100644
--- a/ports/zephyr/mpconfigport.h
+++ b/ports/zephyr/mpconfigport.h
@@ -100,6 +100,7 @@
 #define MICROPY_PY_TIME_INCLUDEFILE "ports/zephyr/modtime.c"
 #define MICROPY_PY_ZEPHYR           (1)
 #define MICROPY_PY_ZSENSOR          (1)
+#define MICROPY_PY_SYS_MAXSIZE      (1)
 #define MICROPY_PY_SYS_STDFILES     (1)
 #define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_MPZ)
 #define MICROPY_FLOAT_IMPL (MICROPY_FLOAT_IMPL_FLOAT)
@@ -150,6 +151,8 @@ typedef long mp_off_t;
 
 #define MP_STATE_PORT MP_STATE_VM
 
+#define MP_SSIZE_MAX (0x7fffffff)
+
 // extra built in names to add to the global namespace
 #define MICROPY_PORT_BUILTINS \
     { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&mp_builtin_open_obj) },