diff --git a/examples/embedding/hello-embed.c b/examples/embedding/hello-embed.c
index 9a90288cf6..0b778986b3 100644
--- a/examples/embedding/hello-embed.c
+++ b/examples/embedding/hello-embed.c
@@ -28,6 +28,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#include "py/builtin.h"
 #include "py/compile.h"
 #include "py/runtime.h"
 #include "py/gc.h"
diff --git a/extmod/vfs.h b/extmod/vfs.h
index 23f2eac893..f577d3e337 100644
--- a/extmod/vfs.h
+++ b/extmod/vfs.h
@@ -26,7 +26,7 @@
 #ifndef MICROPY_INCLUDED_EXTMOD_VFS_H
 #define MICROPY_INCLUDED_EXTMOD_VFS_H
 
-#include "py/lexer.h"
+#include "py/builtin.h"
 #include "py/obj.h"
 
 // return values of mp_vfs_lookup_path
diff --git a/mpy-cross/main.c b/mpy-cross/main.c
index 390689fcbe..f3ffff61fd 100644
--- a/mpy-cross/main.c
+++ b/mpy-cross/main.c
@@ -29,6 +29,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 
+#include "py/builtin.h"
 #include "py/compile.h"
 #include "py/persistentcode.h"
 #include "py/runtime.h"
diff --git a/ports/esp8266/main.c b/ports/esp8266/main.c
index 1ae3f85bff..ded5e58abf 100644
--- a/ports/esp8266/main.c
+++ b/ports/esp8266/main.c
@@ -28,6 +28,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "py/builtin.h"
 #include "py/compile.h"
 #include "py/runtime.h"
 #include "py/stackctrl.h"
diff --git a/ports/javascript/main.c b/ports/javascript/main.c
index 04a853f66c..36ea9e98be 100644
--- a/ports/javascript/main.c
+++ b/ports/javascript/main.c
@@ -29,6 +29,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "py/builtin.h"
 #include "py/compile.h"
 #include "py/runtime.h"
 #include "py/repl.h"
diff --git a/ports/minimal/main.c b/ports/minimal/main.c
index 006ca0a4d0..dbde33915a 100644
--- a/ports/minimal/main.c
+++ b/ports/minimal/main.c
@@ -2,6 +2,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "py/builtin.h"
 #include "py/compile.h"
 #include "py/runtime.h"
 #include "py/repl.h"
diff --git a/ports/nrf/modules/uos/microbitfs.h b/ports/nrf/modules/uos/microbitfs.h
index 4157e8c33d..d9efaabf10 100644
--- a/ports/nrf/modules/uos/microbitfs.h
+++ b/ports/nrf/modules/uos/microbitfs.h
@@ -27,6 +27,7 @@
 #ifndef __MICROPY_INCLUDED_FILESYSTEM_H__
 #define __MICROPY_INCLUDED_FILESYSTEM_H__
 
+#include "py/builtin.h"
 #include "py/obj.h"
 #include "py/lexer.h"
 
diff --git a/ports/powerpc/main.c b/ports/powerpc/main.c
index a66d737c13..ed82c517eb 100644
--- a/ports/powerpc/main.c
+++ b/ports/powerpc/main.c
@@ -26,6 +26,7 @@
 
 #include <stdio.h>
 
+#include "py/builtin.h"
 #include "py/compile.h"
 #include "py/runtime.h"
 #include "py/repl.h"
diff --git a/ports/qemu-arm/test_main.c b/ports/qemu-arm/test_main.c
index 284b287311..3a89b3f131 100644
--- a/ports/qemu-arm/test_main.c
+++ b/ports/qemu-arm/test_main.c
@@ -5,7 +5,7 @@
 #include <malloc.h>
 #include <setjmp.h>
 
-#include "py/obj.h"
+#include "py/builtin.h"
 #include "py/compile.h"
 #include "py/runtime.h"
 #include "py/stackctrl.h"
diff --git a/ports/teensy/lexerfrozen.c b/ports/teensy/lexerfrozen.c
index 21e978dc79..672a0ce08b 100644
--- a/ports/teensy/lexerfrozen.c
+++ b/ports/teensy/lexerfrozen.c
@@ -1,5 +1,6 @@
 #include <stdio.h>
 
+#include "py/builtin.h"
 #include "py/lexer.h"
 #include "py/runtime.h"
 #include "py/mperrno.h"
diff --git a/ports/zephyr/main.c b/ports/zephyr/main.c
index 1275a49739..ed1ac560e1 100644
--- a/ports/zephyr/main.c
+++ b/ports/zephyr/main.c
@@ -41,6 +41,7 @@
 #include <storage/flash_map.h>
 
 #include "py/mperrno.h"
+#include "py/builtin.h"
 #include "py/compile.h"
 #include "py/runtime.h"
 #include "py/repl.h"
diff --git a/py/builtin.h b/py/builtin.h
index 162fed77cc..a6f824ca20 100644
--- a/py/builtin.h
+++ b/py/builtin.h
@@ -28,8 +28,43 @@
 
 #include "py/obj.h"
 
-mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args);
+typedef enum {
+    MP_IMPORT_STAT_NO_EXIST,
+    MP_IMPORT_STAT_DIR,
+    MP_IMPORT_STAT_FILE,
+} mp_import_stat_t;
+
+#if MICROPY_VFS
+
+// Delegate to the VFS for import stat and builtin open.
+
+#define mp_builtin_open_obj mp_vfs_open_obj
+
+mp_import_stat_t mp_vfs_import_stat(const char *path);
+mp_obj_t mp_vfs_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
+
+MP_DECLARE_CONST_FUN_OBJ_KW(mp_vfs_open_obj);
+
+static inline mp_import_stat_t mp_import_stat(const char *path) {
+    return mp_vfs_import_stat(path);
+}
+
+static inline mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+    return mp_vfs_open(n_args, args, kwargs);
+}
+
+#else
+
+// A port can provide implementations of these functions.
+mp_import_stat_t mp_import_stat(const char *path);
 mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
+
+// A port can provide this object.
+MP_DECLARE_CONST_FUN_OBJ_KW(mp_builtin_open_obj);
+
+#endif
+
+mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args);
 mp_obj_t mp_micropython_mem_info(size_t n_args, const mp_obj_t *args);
 
 MP_DECLARE_CONST_FUN_OBJ_VAR(mp_builtin___build_class___obj);
@@ -76,9 +111,7 @@ MP_DECLARE_CONST_FUN_OBJ_1(mp_builtin_repr_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_round_obj);
 MP_DECLARE_CONST_FUN_OBJ_KW(mp_builtin_sorted_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_sum_obj);
-// Defined by a port, but declared here for simplicity
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_input_obj);
-MP_DECLARE_CONST_FUN_OBJ_KW(mp_builtin_open_obj);
 
 MP_DECLARE_CONST_FUN_OBJ_2(mp_namedtuple_obj);
 
diff --git a/py/frozenmod.h b/py/frozenmod.h
index be735e85bd..cff6c8616c 100644
--- a/py/frozenmod.h
+++ b/py/frozenmod.h
@@ -27,7 +27,7 @@
 #ifndef MICROPY_INCLUDED_PY_FROZENMOD_H
 #define MICROPY_INCLUDED_PY_FROZENMOD_H
 
-#include "py/lexer.h"
+#include "py/builtin.h"
 
 enum {
     MP_FROZEN_NONE,
diff --git a/py/lexer.h b/py/lexer.h
index e16b9a8ce8..8295dec0f7 100644
--- a/py/lexer.h
+++ b/py/lexer.h
@@ -189,24 +189,15 @@ typedef struct _mp_lexer_t {
 mp_lexer_t *mp_lexer_new(qstr src_name, mp_reader_t reader);
 mp_lexer_t *mp_lexer_new_from_str_len(qstr src_name, const char *str, size_t len, size_t free_len);
 
-void mp_lexer_free(mp_lexer_t *lex);
-void mp_lexer_to_next(mp_lexer_t *lex);
-
-/******************************************************************/
-// platform specific import function; must be implemented for a specific port
-// TODO tidy up, rename, or put elsewhere
-
-typedef enum {
-    MP_IMPORT_STAT_NO_EXIST,
-    MP_IMPORT_STAT_DIR,
-    MP_IMPORT_STAT_FILE,
-} mp_import_stat_t;
-
-mp_import_stat_t mp_import_stat(const char *path);
+// If MICROPY_READER_POSIX or MICROPY_READER_VFS aren't enabled then
+// this function must be implemented by the port.
 mp_lexer_t *mp_lexer_new_from_file(const char *filename);
 
 #if MICROPY_HELPER_LEXER_UNIX
 mp_lexer_t *mp_lexer_new_from_fd(qstr filename, int fd, bool close_fd);
 #endif
 
+void mp_lexer_free(mp_lexer_t *lex);
+void mp_lexer_to_next(mp_lexer_t *lex);
+
 #endif // MICROPY_INCLUDED_PY_LEXER_H
diff --git a/py/modbuiltins.c b/py/modbuiltins.c
index 5631798fb6..adb9ea40ad 100644
--- a/py/modbuiltins.c
+++ b/py/modbuiltins.c
@@ -729,6 +729,9 @@ STATIC const mp_rom_map_elem_t mp_module_builtins_globals_table[] = {
     #endif
     { MP_ROM_QSTR(MP_QSTR_next), MP_ROM_PTR(&mp_builtin_next_obj) },
     { MP_ROM_QSTR(MP_QSTR_oct), MP_ROM_PTR(&mp_builtin_oct_obj) },
+    #if MICROPY_PY_IO
+    { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&mp_builtin_open_obj) },
+    #endif
     { MP_ROM_QSTR(MP_QSTR_ord), MP_ROM_PTR(&mp_builtin_ord_obj) },
     { MP_ROM_QSTR(MP_QSTR_pow), MP_ROM_PTR(&mp_builtin_pow_obj) },
     { MP_ROM_QSTR(MP_QSTR_print), MP_ROM_PTR(&mp_builtin_print_obj) },