diff --git a/osx.c b/osx.c
index 98cb2c9..23879c1 100644
--- a/osx.c
+++ b/osx.c
@@ -24,11 +24,13 @@
 #ifdef _WIN32
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/locking.h>
 #include <direct.h>
 #include <fcntl.h>
 #include <windows.h>
 #include <io.h>
 #include <share.h>
+#include <limits.h>
 
 typedef struct __stat64 os_stat_type;
 
@@ -75,6 +77,39 @@ static int truncate(const char *path, __int64 size)
 #define ftruncate(fd, size) _chsize_s(fd, size)
 #define fsync(fd) _commit(fd)
 
+static int flocking(FILE *fh, int mode, __int64 ofs, __int64 len)
+{
+    if (ofs < 0 || len < 0 || len > LONG_MAX) {
+        errno = ERANGE;
+        return -1;
+    }
+
+    _lock_file(fh);
+    if (_fseeki64_nolock(fh, ofs, SEEK_SET) != 0)
+        goto fail;
+
+    if (len == 0) {
+        // NOTE: seek may flush write buffers, so file length must be taken now
+        len = _filelengthi64(_fileno(fh));
+        if (len < 0)
+            goto fail;
+        if (len > LONG_MAX) {
+            errno = ERANGE;
+            goto fail;
+        }
+    }
+
+    if (_locking(_fileno(fh), mode, len) != 0)
+        goto fail;
+
+    _unlock_file(fh);
+    return 0;
+
+fail:
+    _unlock_file(fh);
+    return -1;
+}
+
 #else
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -106,6 +141,39 @@ static inline int setmode(int fd, int mode)
     errno = ENOTSUP;
     return -1;
 }
+
+#define _LK_NBRLCK F_RDLCK
+#define _LK_NBLCK F_WRLCK
+#define _LK_UNLCK F_UNLCK
+
+static int flocking(FILE *fh, int mode, off_t ofs, off_t len)
+{
+    if (ofs < 0 || len < 0) {
+        errno = ERANGE;
+        return -1;
+    }
+
+    flockfile(fh);
+
+    if (fseeko(fh, ofs, SEEK_SET) != 0)
+        goto fail;
+
+    struct flock lk = {
+        .l_whence = SEEK_SET,
+        .l_type = mode,
+        .l_start = ofs,
+        .l_len = len  // NOTE: 0 has special meaning
+    };
+    if (fcntl(fileno(fh), F_SETLK, &lk) != 0)
+        goto fail;
+
+    funlockfile(fh);
+    return 0;
+
+fail:
+    funlockfile(fh);
+    return -1;
+}
 #endif
 
 #ifdef __linux__
@@ -538,6 +606,20 @@ static int os_commit(lua_State *L)
     return os_result(L, ec, NULL);
 }
 
+static int os_locking(lua_State *L)
+{
+    static const char *modes[] = { "r", "w", "u", NULL };
+    static const int imodes[] = { _LK_NBRLCK, _LK_NBLCK, _LK_UNLCK };
+
+    luaL_Stream *stream = luaL_checkudata(L, 1, LUA_FILEHANDLE);
+    int i = luaL_checkoption(L, 2, NULL, modes);
+    lua_Integer ofs = luaL_optinteger(L, 3, 0);
+    lua_Integer len = luaL_optinteger(L, 4, 0);
+
+    int ec = flocking(stream->f, imodes[i], ofs, len);
+    return os_result(L, ec, NULL);
+}
+
 static void createmeta(lua_State *L)
 {
     static const luaL_Reg metameth[] = {
@@ -579,6 +661,7 @@ DF_OSXMOD_API int luaopen_osx(lua_State *L)
         { "chsize", os_chsize },
         { "fadvise", os_fadvise },
         { "commit", os_commit },
+        { "locking", os_locking },
         { NULL, NULL }
     };