diff --git a/py/modstruct.c b/py/modstruct.c
index 42f91b282..b3edc9632 100644
--- a/py/modstruct.c
+++ b/py/modstruct.c
@@ -92,7 +92,9 @@ STATIC size_t calc_size_items(const char *fmt, size_t *total_sz) {
             cnt = get_fmt_num(&fmt);
         }
 
-        if (*fmt == 's') {
+        if (*fmt == 'x') {
+            size += cnt;
+        } else if (*fmt == 's') {
             total_cnt += 1;
             size += cnt;
         } else {
@@ -159,7 +161,9 @@ STATIC mp_obj_t struct_unpack_from(size_t n_args, const mp_obj_t *args) {
             cnt = get_fmt_num(&fmt);
         }
         mp_obj_t item;
-        if (*fmt == 's') {
+        if (*fmt == 'x') {
+            p += cnt;
+        } else if (*fmt == 's') {
             item = mp_obj_new_bytes(p, cnt);
             p += cnt;
             res->items[i++] = item;
@@ -192,7 +196,10 @@ STATIC void struct_pack_into_internal(mp_obj_t fmt_in, byte *p, size_t n_args, c
             cnt = get_fmt_num(&fmt);
         }
 
-        if (*fmt == 's') {
+        if (*fmt == 'x') {
+            memset(p, 0, cnt);
+            p += cnt;
+        } else if (*fmt == 's') {
             mp_buffer_info_t bufinfo;
             mp_get_buffer_raise(args[i++], &bufinfo, MP_BUFFER_READ);
             mp_uint_t to_copy = cnt;
diff --git a/tests/basics/struct1.py b/tests/basics/struct1.py
index a18655517..e473ffcc1 100644
--- a/tests/basics/struct1.py
+++ b/tests/basics/struct1.py
@@ -20,6 +20,8 @@ print(struct.pack("<h", 1))
 print(struct.pack(">h", 1))
 print(struct.pack("<b", 1))
 print(struct.pack(">b", 1))
+print(struct.pack("<x"))
+print(struct.pack(">x"))
 
 print(struct.pack("<bI", -128, 256))
 print(struct.pack(">bI", -128, 256))
@@ -29,6 +31,13 @@ print(struct.calcsize("97sI"))
 print(struct.unpack("<6sH", b"foo\0\0\0\x12\x34"))
 print(struct.pack("<6sH", b"foo", 10000))
 
+print(struct.calcsize("7xx"))
+print(struct.pack("7xx"))
+
+print(struct.calcsize(">bxI3xH"))
+print(struct.pack(">bxI3xH", 1, 2, 3))
+print(struct.unpack(">bxI3xH", b"\x01\0\0\0\0\x02\0\0\0\0\x03"))
+
 s = struct.pack("BHBI", 10, 100, 200, 300)
 v = struct.unpack("BHBI", s)
 print(v == (10, 100, 200, 300))