diff --git a/mypy/typeshed/stubs/librt/librt/internal.pyi b/mypy/typeshed/stubs/librt/librt/internal.pyi
index a47a4849fe20..8a5fc262931e 100644
--- a/mypy/typeshed/stubs/librt/librt/internal.pyi
+++ b/mypy/typeshed/stubs/librt/librt/internal.pyi
@@ -8,6 +8,8 @@ def write_bool(data: Buffer, value: bool) -> None: ...
 def read_bool(data: Buffer) -> bool: ...
 def write_str(data: Buffer, value: str) -> None: ...
 def read_str(data: Buffer) -> str: ...
+def write_bytes(data: Buffer, value: bytes) -> None: ...
+def read_bytes(data: Buffer) -> bytes: ...
 def write_float(data: Buffer, value: float) -> None: ...
 def read_float(data: Buffer) -> float: ...
 def write_int(data: Buffer, value: int) -> None: ...
diff --git a/mypyc/lib-rt/librt_internal.c b/mypyc/lib-rt/librt_internal.c
index b97d6665b515..6f6a110446ad 100644
--- a/mypyc/lib-rt/librt_internal.c
+++ b/mypyc/lib-rt/librt_internal.c
@@ -346,6 +346,100 @@ write_str(PyObject *self, PyObject *const *args, size_t nargs, PyObject *kwnames
     return Py_None;
 }
 
+/*
+bytes format: size followed by bytes
+    short bytes (len <= 127): single byte for size as `(uint8_t)size << 1`
+    long bytes: \x01 followed by size as Py_ssize_t
+*/
+
+static PyObject*
+read_bytes_internal(PyObject *data) {
+    _CHECK_BUFFER(data, NULL)
+
+    // Read length.
+    Py_ssize_t size;
+    _CHECK_READ(data, 1, NULL)
+    uint8_t first = _READ(data, uint8_t)
+    if (likely(first != LONG_STR_TAG)) {
+        // Common case: short bytes (len <= 127).
+        size = (Py_ssize_t)(first >> 1);
+    } else {
+        _CHECK_READ(data, sizeof(CPyTagged), NULL)
+        size = _READ(data, Py_ssize_t)
+    }
+    // Read bytes content.
+    char *buf = ((BufferObject *)data)->buf;
+    _CHECK_READ(data, size, NULL)
+    PyObject *res = PyBytes_FromStringAndSize(
+        buf + ((BufferObject *)data)->pos, (Py_ssize_t)size
+    );
+    if (unlikely(res == NULL))
+        return NULL;
+    ((BufferObject *)data)->pos += size;
+    return res;
+}
+
+static PyObject*
+read_bytes(PyObject *self, PyObject *const *args, size_t nargs, PyObject *kwnames) {
+    static const char * const kwlist[] = {"data", 0};
+    static CPyArg_Parser parser = {"O:read_bytes", kwlist, 0};
+    PyObject *data;
+    if (unlikely(!CPyArg_ParseStackAndKeywordsOneArg(args, nargs, kwnames, &parser, &data))) {
+        return NULL;
+    }
+    return read_bytes_internal(data);
+}
+
+static char
+write_bytes_internal(PyObject *data, PyObject *value) {
+    _CHECK_BUFFER(data, CPY_NONE_ERROR)
+
+    const char *chunk = PyBytes_AsString(value);
+    if (unlikely(chunk == NULL))
+        return CPY_NONE_ERROR;
+    Py_ssize_t size = PyBytes_GET_SIZE(value);
+
+    Py_ssize_t need;
+    // Write length.
+    if (likely(size <= MAX_SHORT_LEN)) {
+        // Common case: short bytes (len <= 127) store as single byte.
+        need = size + 1;
+        _CHECK_SIZE(data, need)
+        _WRITE(data, uint8_t, (uint8_t)size << 1)
+    } else {
+        need = size + sizeof(Py_ssize_t) + 1;
+        _CHECK_SIZE(data, need)
+        _WRITE(data, uint8_t, LONG_STR_TAG)
+        _WRITE(data, Py_ssize_t, size)
+    }
+    // Write bytes content.
+    char *buf = ((BufferObject *)data)->buf;
+    memcpy(buf + ((BufferObject *)data)->pos, chunk, size);
+    ((BufferObject *)data)->pos += size;
+    ((BufferObject *)data)->end += need;
+    return CPY_NONE;
+}
+
+static PyObject*
+write_bytes(PyObject *self, PyObject *const *args, size_t nargs, PyObject *kwnames) {
+    static const char * const kwlist[] = {"data", "value", 0};
+    static CPyArg_Parser parser = {"OO:write_bytes", kwlist, 0};
+    PyObject *data;
+    PyObject *value;
+    if (unlikely(!CPyArg_ParseStackAndKeywordsSimple(args, nargs, kwnames, &parser, &data, &value))) {
+        return NULL;
+    }
+    if (unlikely(!PyBytes_Check(value))) {
+        PyErr_SetString(PyExc_TypeError, "value must be a bytes object");
+        return NULL;
+    }
+    if (unlikely(write_bytes_internal(data, value) == CPY_NONE_ERROR)) {
+        return NULL;
+    }
+    Py_INCREF(Py_None);
+    return Py_None;
+}
+
 /*
 float format:
     stored as a C double
@@ -565,6 +659,8 @@ static PyMethodDef librt_internal_module_methods[] = {
     {"read_bool", (PyCFunction)read_bool, METH_FASTCALL | METH_KEYWORDS, PyDoc_STR("read a bool")},
     {"write_str", (PyCFunction)write_str, METH_FASTCALL | METH_KEYWORDS, PyDoc_STR("write a string")},
     {"read_str", (PyCFunction)read_str, METH_FASTCALL | METH_KEYWORDS, PyDoc_STR("read a string")},
+    {"write_bytes", (PyCFunction)write_bytes, METH_FASTCALL | METH_KEYWORDS, PyDoc_STR("write bytes")},
+    {"read_bytes", (PyCFunction)read_bytes, METH_FASTCALL | METH_KEYWORDS, PyDoc_STR("read bytes")},
     {"write_float", (PyCFunction)write_float, METH_FASTCALL | METH_KEYWORDS, PyDoc_STR("write a float")},
     {"read_float", (PyCFunction)read_float, METH_FASTCALL | METH_KEYWORDS, PyDoc_STR("read a float")},
     {"write_int", (PyCFunction)write_int, METH_FASTCALL | METH_KEYWORDS, PyDoc_STR("write an int")},
@@ -590,7 +686,7 @@ librt_internal_module_exec(PyObject *m)
     }
 
     // Export mypy internal C API, be careful with the order!
-    static void *NativeInternal_API[14] = {
+    static void *NativeInternal_API[16] = {
         (void *)Buffer_internal,
         (void *)Buffer_internal_empty,
         (void *)Buffer_getvalue_internal,
@@ -605,6 +701,8 @@ librt_internal_module_exec(PyObject *m)
         (void *)write_tag_internal,
         (void *)read_tag_internal,
         (void *)NativeInternal_ABI_Version,
+        (void *)write_bytes_internal,
+        (void *)read_bytes_internal,
     };
     PyObject *c_api_object = PyCapsule_New((void *)NativeInternal_API, "librt.internal._C_API", NULL);
     if (PyModule_Add(m, "_C_API", c_api_object) < 0) {
diff --git a/mypyc/lib-rt/librt_internal.h b/mypyc/lib-rt/librt_internal.h
index fd8ec2422cc5..d996b8fd95c1 100644
--- a/mypyc/lib-rt/librt_internal.h
+++ b/mypyc/lib-rt/librt_internal.h
@@ -19,6 +19,8 @@ static CPyTagged read_int_internal(PyObject *data);
 static char write_tag_internal(PyObject *data, uint8_t value);
 static uint8_t read_tag_internal(PyObject *data);
 static int NativeInternal_ABI_Version(void);
+static char write_bytes_internal(PyObject *data, PyObject *value);
+static PyObject *read_bytes_internal(PyObject *data);
 
 #else
 
@@ -38,6 +40,8 @@ static void **NativeInternal_API;
 #define write_tag_internal (*(char (*)(PyObject *source, uint8_t value)) NativeInternal_API[11])
 #define read_tag_internal (*(uint8_t (*)(PyObject *source)) NativeInternal_API[12])
 #define NativeInternal_ABI_Version (*(int (*)(void)) NativeInternal_API[13])
+#define write_bytes_internal (*(char (*)(PyObject *source, PyObject *value)) NativeInternal_API[14])
+#define read_bytes_internal (*(PyObject* (*)(PyObject *source)) NativeInternal_API[15])
 
 static int
 import_librt_internal(void)
diff --git a/mypyc/primitives/misc_ops.py b/mypyc/primitives/misc_ops.py
index 18d475fe89d4..c12172875e8b 100644
--- a/mypyc/primitives/misc_ops.py
+++ b/mypyc/primitives/misc_ops.py
@@ -393,6 +393,22 @@
     error_kind=ERR_MAGIC,
 )
 
+function_op(
+    name="librt.internal.write_bytes",
+    arg_types=[object_rprimitive, bytes_rprimitive],
+    return_type=none_rprimitive,
+    c_function_name="write_bytes_internal",
+    error_kind=ERR_MAGIC,
+)
+
+function_op(
+    name="librt.internal.read_bytes",
+    arg_types=[object_rprimitive],
+    return_type=bytes_rprimitive,
+    c_function_name="read_bytes_internal",
+    error_kind=ERR_MAGIC,
+)
+
 function_op(
     name="librt.internal.write_float",
     arg_types=[object_rprimitive, float_rprimitive],
diff --git a/mypyc/test-data/irbuild-classes.test b/mypyc/test-data/irbuild-classes.test
index 3280b21cf7e6..27ffba45ba39 100644
--- a/mypyc/test-data/irbuild-classes.test
+++ b/mypyc/test-data/irbuild-classes.test
@@ -1454,7 +1454,7 @@ from typing import Final
 from mypy_extensions import u8
 from librt.internal import (
     Buffer, write_bool, read_bool, write_str, read_str, write_float, read_float,
-    write_int, read_int, write_tag, read_tag
+    write_int, read_int, write_tag, read_tag, write_bytes, read_bytes,
 )
 
 Tag = u8
@@ -1463,6 +1463,7 @@ TAG: Final[Tag] = 1
 def foo() -> None:
     b = Buffer()
     write_str(b, "foo")
+    write_bytes(b, b"bar")
     write_bool(b, True)
     write_float(b, 0.1)
     write_int(b, 1)
@@ -1470,6 +1471,7 @@ def foo() -> None:
 
     b = Buffer(b.getvalue())
     x = read_str(b)
+    xb = read_bytes(b)
     y = read_bool(b)
     z = read_float(b)
     t = read_int(b)
@@ -1478,36 +1480,43 @@ def foo() -> None:
 def foo():
     r0, b :: librt.internal.Buffer
     r1 :: str
-    r2, r3, r4, r5, r6 :: None
-    r7 :: bytes
-    r8 :: librt.internal.Buffer
-    r9, x :: str
-    r10, y :: bool
-    r11, z :: float
-    r12, t :: int
-    r13, u :: u8
+    r2 :: None
+    r3 :: bytes
+    r4, r5, r6, r7, r8 :: None
+    r9 :: bytes
+    r10 :: librt.internal.Buffer
+    r11, x :: str
+    r12, xb :: bytes
+    r13, y :: bool
+    r14, z :: float
+    r15, t :: int
+    r16, u :: u8
 L0:
     r0 = Buffer_internal_empty()
     b = r0
     r1 = 'foo'
     r2 = write_str_internal(b, r1)
-    r3 = write_bool_internal(b, 1)
-    r4 = write_float_internal(b, 0.1)
-    r5 = write_int_internal(b, 2)
-    r6 = write_tag_internal(b, 1)
-    r7 = Buffer_getvalue_internal(b)
-    r8 = Buffer_internal(r7)
-    b = r8
-    r9 = read_str_internal(b)
-    x = r9
-    r10 = read_bool_internal(b)
-    y = r10
-    r11 = read_float_internal(b)
-    z = r11
-    r12 = read_int_internal(b)
-    t = r12
-    r13 = read_tag_internal(b)
-    u = r13
+    r3 = b'bar'
+    r4 = write_bytes_internal(b, r3)
+    r5 = write_bool_internal(b, 1)
+    r6 = write_float_internal(b, 0.1)
+    r7 = write_int_internal(b, 2)
+    r8 = write_tag_internal(b, 1)
+    r9 = Buffer_getvalue_internal(b)
+    r10 = Buffer_internal(r9)
+    b = r10
+    r11 = read_str_internal(b)
+    x = r11
+    r12 = read_bytes_internal(b)
+    xb = r12
+    r13 = read_bool_internal(b)
+    y = r13
+    r14 = read_float_internal(b)
+    z = r14
+    r15 = read_int_internal(b)
+    t = r15
+    r16 = read_tag_internal(b)
+    u = r16
     return 1
 
 [case testEnumFastPath]
diff --git a/mypyc/test-data/run-classes.test b/mypyc/test-data/run-classes.test
index 84704ce66c81..efa6c225ecab 100644
--- a/mypyc/test-data/run-classes.test
+++ b/mypyc/test-data/run-classes.test
@@ -2715,7 +2715,7 @@ from typing import Final
 from mypy_extensions import u8
 from librt.internal import (
     Buffer, write_bool, read_bool, write_str, read_str, write_float, read_float,
-    write_int, read_int, write_tag, read_tag
+    write_int, read_int, write_tag, read_tag, write_bytes, read_bytes
 )
 
 Tag = u8
@@ -2733,6 +2733,11 @@ def test_buffer_roundtrip() -> None:
     write_bool(b, True)
     write_str(b, "bar" * 1000)
     write_bool(b, False)
+    write_bytes(b, b"bar")
+    write_bytes(b, b"bar" * 100)
+    write_bytes(b, b"")
+    write_bytes(b, b"a" * 127)
+    write_bytes(b, b"a" * 128)
     write_float(b, 0.1)
     write_int(b, 0)
     write_int(b, 1)
@@ -2752,6 +2757,11 @@ def test_buffer_roundtrip() -> None:
     assert read_bool(b) is True
     assert read_str(b) == "bar" * 1000
     assert read_bool(b) is False
+    assert read_bytes(b) == b"bar"
+    assert read_bytes(b) == b"bar" * 100
+    assert read_bytes(b) == b""
+    assert read_bytes(b) == b"a" * 127
+    assert read_bytes(b) == b"a" * 128
     assert read_float(b) == 0.1
     assert read_int(b) == 0
     assert read_int(b) == 1
@@ -2806,6 +2816,11 @@ def test_buffer_roundtrip_interpreted() -> None:
     write_bool(b, True)
     write_str(b, "bar" * 1000)
     write_bool(b, False)
+    write_bytes(b, b"bar")
+    write_bytes(b, b"bar" * 100)
+    write_bytes(b, b"")
+    write_bytes(b, b"a" * 127)
+    write_bytes(b, b"a" * 128)
     write_float(b, 0.1)
     write_int(b, 0)
     write_int(b, 1)
@@ -2825,6 +2840,11 @@ def test_buffer_roundtrip_interpreted() -> None:
     assert read_bool(b) is True
     assert read_str(b) == "bar" * 1000
     assert read_bool(b) is False
+    assert read_bytes(b) == b"bar"
+    assert read_bytes(b) == b"bar" * 100
+    assert read_bytes(b) == b""
+    assert read_bytes(b) == b"a" * 127
+    assert read_bytes(b) == b"a" * 128
     assert read_float(b) == 0.1
     assert read_int(b) == 0
     assert read_int(b) == 1