diff -r d8391a8714ca ocaml/otherlibs/unix/stat.c
--- a/ocaml/otherlibs/unix/stat.c
+++ b/ocaml/otherlibs/unix/stat.c
@@ -74,7 +74,9 @@
 {
   int ret;
   struct stat buf;
+  caml_enter_blocking_section();
   ret = stat(String_val(path), &buf);
+  caml_leave_blocking_section();
   if (ret == -1) uerror("stat", path);
   if (buf.st_size > Max_long && (buf.st_mode & S_IFMT) == S_IFREG)
     unix_error(EOVERFLOW, "stat", path);
@@ -85,11 +87,13 @@
 {
   int ret;
   struct stat buf;
+  caml_enter_blocking_section();
 #ifdef HAS_SYMLINK
   ret = lstat(String_val(path), &buf);
 #else
   ret = stat(String_val(path), &buf);
 #endif
+  caml_leave_blocking_section();
   if (ret == -1) uerror("lstat", path);
   if (buf.st_size > Max_long && (buf.st_mode & S_IFMT) == S_IFREG)
     unix_error(EOVERFLOW, "lstat", path);
@@ -100,7 +104,9 @@
 {
   int ret;
   struct stat buf;
+  caml_enter_blocking_section();
   ret = fstat(Int_val(fd), &buf);
+  caml_leave_blocking_section();
   if (ret == -1) uerror("fstat", Nothing);
   if (buf.st_size > Max_long && (buf.st_mode & S_IFMT) == S_IFREG)
     unix_error(EOVERFLOW, "fstat", Nothing);
@@ -111,7 +117,9 @@
 {
   int ret;
   struct stat buf;
+  caml_enter_blocking_section();
   ret = stat(String_val(path), &buf);
+  caml_leave_blocking_section();
   if (ret == -1) uerror("stat", path);
   return stat_aux(1, &buf);
 }
@@ -120,11 +128,13 @@
 {
   int ret;
   struct stat buf;
+  caml_enter_blocking_section();
 #ifdef HAS_SYMLINK
   ret = lstat(String_val(path), &buf);
 #else
   ret = stat(String_val(path), &buf);
 #endif
+  caml_leave_blocking_section();
   if (ret == -1) uerror("lstat", path);
   return stat_aux(1, &buf);
 }
@@ -133,7 +143,9 @@
 {
   int ret;
   struct stat buf;
+  caml_enter_blocking_section();
   ret = fstat(Int_val(fd), &buf);
+  caml_leave_blocking_section();
   if (ret == -1) uerror("fstat", Nothing);
   return stat_aux(1, &buf);
 }
diff -r 2ae9b39aa4c0 ocaml/byterun/sys.c
--- a/ocaml/byterun/sys.c
+++ b/ocaml/byterun/sys.c
@@ -156,13 +156,21 @@
 CAMLprim value caml_sys_file_exists(value name)
 {
   struct stat st;
-  return Val_bool(stat(String_val(name), &st) == 0);
+  int res;
+  caml_enter_blocking_section();
+  res = stat(String_val(name), &st);
+  caml_leave_blocking_section();
+  return Val_bool(res == 0);
 }
 
 CAMLprim value caml_sys_is_directory(value name)
 {
   struct stat st;
-  if (stat(String_val(name), &st) == -1) caml_sys_error(name);
+  int res;
+  caml_enter_blocking_section();
+  res = stat(String_val(name), &st);
+  caml_leave_blocking_section();
+  if (res == -1) caml_sys_error(name);
 #ifdef S_ISDIR
   return Val_bool(S_ISDIR(st.st_mode));
 #else