diff --git a/py/objarray.c b/py/objarray.c
index 0383cb17b3..4f9fa49bcb 100644
--- a/py/objarray.c
+++ b/py/objarray.c
@@ -91,6 +91,13 @@ STATIC mp_obj_t array_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const m
 // This is top-level factory function, not virtual method
 // TODO: "bytearray" really should be type, not function
 STATIC mp_obj_t mp_builtin_bytearray(mp_obj_t arg) {
+    if (MP_OBJ_IS_SMALL_INT(arg)) {
+        uint len = MP_OBJ_SMALL_INT_VALUE(arg);
+        mp_obj_array_t *o = array_new(BYTEARRAY_TYPECODE, len);
+        memset(o->items, 0, len);
+        return o;
+    }
+
     return array_construct(BYTEARRAY_TYPECODE, arg);
 }
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_bytearray_obj, mp_builtin_bytearray);
diff --git a/py/objstr.c b/py/objstr.c
index d2d672b983..5e9f0c76b6 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -1352,6 +1352,7 @@ const mp_obj_type_t mp_type_bytes = {
     .make_new = bytes_make_new,
     .binary_op = str_binary_op,
     .getiter = mp_obj_new_bytes_iterator,
+    .buffer_p = { .get_buffer = str_get_buffer },
     .locals_dict = (mp_obj_t)&str_locals_dict,
 };
 
diff --git a/tests/basics/bytearray1.py b/tests/basics/bytearray1.py
index 3111832f6c..201b5b6590 100644
--- a/tests/basics/bytearray1.py
+++ b/tests/basics/bytearray1.py
@@ -1,3 +1,4 @@
+print(bytearray(4))
 a = bytearray([1, 2, 200])
 print(a[0], a[2])
 print(a[-1])
diff --git a/unix/modffi.c b/unix/modffi.c
index dd4c7012f7..8764cb7c9e 100644
--- a/unix/modffi.c
+++ b/unix/modffi.c
@@ -253,14 +253,22 @@ mp_obj_t ffifunc_call(mp_obj_t self_in, uint n_args, uint n_kw, const mp_obj_t *
             values[i] = 0;
         } else if (MP_OBJ_IS_INT(a)) {
             values[i] = mp_obj_int_get(a);
-        } else if (MP_OBJ_IS_STR(a) || MP_OBJ_IS_TYPE(a, &mp_type_bytes)) {
+        } else if (MP_OBJ_IS_STR(a)) {
             const char *s = mp_obj_str_get_str(a);
             values[i] = (ffi_arg)s;
+        } else if (((mp_obj_base_t*)a)->type->buffer_p.get_buffer != NULL) {
+            mp_obj_base_t *o = (mp_obj_base_t*)a;
+            buffer_info_t bufinfo;
+            o->type->buffer_p.get_buffer(o, &bufinfo, BUFFER_READ); // TODO: BUFFER_READ?
+            if (bufinfo.buf == NULL) {
+                goto error;
+            }
+            values[i] = (ffi_arg)bufinfo.buf;
         } else if (MP_OBJ_IS_TYPE(a, &fficallback_type)) {
             mp_obj_fficallback_t *p = a;
             values[i] = (ffi_arg)p->func;
         } else {
-            assert(0);
+            goto error;
         }
         valueptrs[i] = &values[i];
     }
@@ -268,6 +276,9 @@ mp_obj_t ffifunc_call(mp_obj_t self_in, uint n_args, uint n_kw, const mp_obj_t *
     ffi_arg retval;
     ffi_call(&self->cif, self->func, &retval, valueptrs);
     return return_ffi_value(retval, self->rettype);
+
+error:
+    nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "Don't know how to pass object to native function"));
 }
 
 STATIC const mp_obj_type_t ffifunc_type = {