diff --git a/lib/fs.c b/lib/fs.c
index 4d9695e3..d0d97acc 100644
--- a/lib/fs.c
+++ b/lib/fs.c
@@ -53,6 +53,7 @@
 #include <unistd.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <sys/file.h>
 #include <grp.h>
 #include <pwd.h>
 #include <glob.h>
@@ -738,6 +739,97 @@ uc_fs_seek(uc_vm_t *vm, size_t nargs)
 	return ucv_boolean_new(true);
 }
 
+/**
+ * Truncate file to a given size
+ *
+ * Returns `true` if the file was successfully truncated.
+ *
+ * Returns `null` if an error occurred.
+ *
+ * @function module:fs.file#truncate
+ *
+ * @param {number} [offset=0]
+ * The offset in bytes.
+ *
+ * @returns {?boolean}
+ */
+static uc_value_t *
+uc_fs_truncate(uc_vm_t *vm, size_t nargs)
+{
+	FILE *fp = uc_fn_thisval("fs.file");
+	uc_value_t *ofs = uc_fn_arg(0);
+	off_t offset;
+
+	if (!fp)
+		err_return(EBADF);
+
+	if (!ofs)
+		offset = 0;
+	else if (ucv_type(ofs) != UC_INTEGER)
+		err_return(EINVAL);
+	else
+		offset = (off_t)ucv_int64_get(ofs);
+
+	if (ftruncate(fileno(fp), offset) < 0)
+		err_return(errno);
+
+	return ucv_boolean_new(true);
+}
+
+/**
+ * Locks or unlocks a file.
+ *
+ * The mode argument specifies lock/unlock operation flags.
+ *
+ * | Flag    | Description                  |
+ * |---------|------------------------------|
+ * | "s"     | shared lock                  |
+ * | "x"     | exclusive lock               |
+ * | "n"     | don't block when locking     |
+ * | "u"     | unlock                       |
+ *
+ * Returns `true` if the file was successfully locked/unlocked.
+ *
+ * Returns `null` if an error occurred.
+ *
+ * @function module:fs.file#lock
+ *
+ * @param {string} [op]
+ * The lock operation flags
+ *
+ * @returns {?boolean}
+ */
+static uc_value_t *
+uc_fs_lock(uc_vm_t *vm, size_t nargs)
+{
+	FILE *fp = uc_fn_thisval("fs.file");
+	uc_value_t *mode = uc_fn_arg(0);
+	int i, op = 0;
+	char *m;
+
+	if (!fp)
+		err_return(EBADF);
+
+	if (ucv_type(mode) != UC_STRING)
+		err_return(EINVAL);
+
+	m = ucv_string_get(mode);
+	for (i = 0; m[i]; i++) {
+		switch (m[i]) {
+		case 's': op |= LOCK_SH; break;
+		case 'x': op |= LOCK_EX; break;
+		case 'n': op |= LOCK_NB; break;
+		case 'u': op |= LOCK_UN; break;
+		default: err_return(EINVAL);
+		}
+	}
+
+	if (flock(fileno(fp), op) < 0)
+		err_return(errno);
+
+	return ucv_boolean_new(true);
+}
+
 /**
  * Obtain current read position.
  *
@@ -2571,6 +2663,8 @@ static const uc_function_list_t file_fns[] = {
 	{ "fileno",		uc_fs_fileno },
 	{ "error",		uc_fs_error },
 	{ "isatty",		uc_fs_isatty },
+	{ "truncate",	uc_fs_truncate },
+	{ "lock",		uc_fs_lock },
 };
 
 static const uc_function_list_t dir_fns[] = {
diff --git a/tests/custom/03_stdlib/40_proto b/tests/custom/03_stdlib/40_proto
index 2a12966b..d96d124b 100644
--- a/tests/custom/03_stdlib/40_proto
+++ b/tests/custom/03_stdlib/40_proto
@@ -38,6 +38,8 @@ When invoked with two arguments, returns the given value.
 Hello, World!
 [
 	{
+		"lock": "function lock(...) { [native code] }",
+		"truncate": "function truncate(...) { [native code] }",
 		"isatty": "function isatty(...) { [native code] }",
 		"error": "function error(...) { [native code] }",
 		"fileno": "function fileno(...) { [native code] }",