diff --git a/py/persistentcode.c b/py/persistentcode.c
index 7a8a94b5a6..7039f9f57a 100644
--- a/py/persistentcode.c
+++ b/py/persistentcode.c
@@ -34,6 +34,7 @@
 #include "py/persistentcode.h"
 #include "py/bc0.h"
 #include "py/objstr.h"
+#include "py/mpthread.h"
 
 #if MICROPY_PERSISTENT_CODE_LOAD || MICROPY_PERSISTENT_CODE_SAVE
 
@@ -821,15 +822,21 @@ void mp_raw_code_save(mp_raw_code_t *rc, mp_print_t *print) {
 
 STATIC void fd_print_strn(void *env, const char *str, size_t len) {
     int fd = (intptr_t)env;
+    MP_THREAD_GIL_EXIT();
     ssize_t ret = write(fd, str, len);
+    MP_THREAD_GIL_ENTER();
     (void)ret;
 }
 
 void mp_raw_code_save_file(mp_raw_code_t *rc, const char *filename) {
+    MP_THREAD_GIL_EXIT();
     int fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+    MP_THREAD_GIL_ENTER();
     mp_print_t fd_print = {(void*)(intptr_t)fd, fd_print_strn};
     mp_raw_code_save(rc, &fd_print);
+    MP_THREAD_GIL_EXIT();
     close(fd);
+    MP_THREAD_GIL_ENTER();
 }
 
 #else
diff --git a/py/reader.c b/py/reader.c
index 80364104bb..d99dfc5672 100644
--- a/py/reader.c
+++ b/py/reader.c
@@ -29,6 +29,7 @@
 
 #include "py/runtime.h"
 #include "py/mperrno.h"
+#include "py/mpthread.h"
 #include "py/reader.h"
 
 typedef struct _mp_reader_mem_t {
@@ -86,7 +87,9 @@ STATIC mp_uint_t mp_reader_posix_readbyte(void *data) {
         if (reader->len == 0) {
             return MP_READER_EOF;
         } else {
+            MP_THREAD_GIL_EXIT();
             int n = read(reader->fd, reader->buf, sizeof(reader->buf));
+            MP_THREAD_GIL_ENTER();
             if (n <= 0) {
                 reader->len = 0;
                 return MP_READER_EOF;
@@ -101,7 +104,9 @@ STATIC mp_uint_t mp_reader_posix_readbyte(void *data) {
 STATIC void mp_reader_posix_close(void *data) {
     mp_reader_posix_t *reader = (mp_reader_posix_t*)data;
     if (reader->close_fd) {
+        MP_THREAD_GIL_EXIT();
         close(reader->fd);
+        MP_THREAD_GIL_ENTER();
     }
     m_del_obj(mp_reader_posix_t, reader);
 }
@@ -110,13 +115,16 @@ void mp_reader_new_file_from_fd(mp_reader_t *reader, int fd, bool close_fd) {
     mp_reader_posix_t *rp = m_new_obj(mp_reader_posix_t);
     rp->close_fd = close_fd;
     rp->fd = fd;
+    MP_THREAD_GIL_EXIT();
     int n = read(rp->fd, rp->buf, sizeof(rp->buf));
     if (n == -1) {
         if (close_fd) {
             close(fd);
         }
+        MP_THREAD_GIL_ENTER();
         mp_raise_OSError(errno);
     }
+    MP_THREAD_GIL_ENTER();
     rp->len = n;
     rp->pos = 0;
     reader->data = rp;
@@ -127,7 +135,9 @@ void mp_reader_new_file_from_fd(mp_reader_t *reader, int fd, bool close_fd) {
 #if !MICROPY_VFS_POSIX
 // If MICROPY_VFS_POSIX is defined then this function is provided by the VFS layer
 void mp_reader_new_file(mp_reader_t *reader, const char *filename) {
+    MP_THREAD_GIL_EXIT();
     int fd = open(filename, O_RDONLY, 0644);
+    MP_THREAD_GIL_ENTER();
     if (fd < 0) {
         mp_raise_OSError(errno);
     }