diff --git a/aioesphomeapi/_frame_helper/plain_text.pxd b/aioesphomeapi/_frame_helper/plain_text.pxd
index b0bd3a1..994804f 100644
--- a/aioesphomeapi/_frame_helper/plain_text.pxd
+++ b/aioesphomeapi/_frame_helper/plain_text.pxd
@@ -7,6 +7,11 @@ cdef bint TYPE_CHECKING
 cdef object WRITE_EXCEPTIONS
 cdef object bytes_to_varuint, varuint_to_bytes
 
+cpdef _varuint_to_bytes(cython.int value)
+
+@cython.locals(result=cython.int, bitpos=cython.int, val=cython.int)
+cpdef _bytes_to_varuint(cython.bytes value)
+
 cdef class APIPlaintextFrameHelper(APIFrameHelper):
 
     @cython.locals(
diff --git a/aioesphomeapi/_frame_helper/plain_text.py b/aioesphomeapi/_frame_helper/plain_text.py
index b9b149b..b629b3e 100644
--- a/aioesphomeapi/_frame_helper/plain_text.py
+++ b/aioesphomeapi/_frame_helper/plain_text.py
@@ -2,14 +2,54 @@ from __future__ import annotations
 
 import asyncio
 import logging
+from functools import lru_cache
 from typing import TYPE_CHECKING
 
 from ..core import ProtocolAPIError, RequiresEncryptionAPIError, SocketAPIError
-from ..util import bytes_to_varuint, varuint_to_bytes
 from .base import WRITE_EXCEPTIONS, APIFrameHelper
 
 _LOGGER = logging.getLogger(__name__)
 
+_int = int
+_bytes = bytes
+
+
+def _varuint_to_bytes(value: _int) -> bytes:
+    """Convert a varuint to bytes."""
+    if value <= 0x7F:
+        return bytes((value,))
+
+    result = []
+    while value:
+        temp = value & 0x7F
+        value >>= 7
+        if value:
+            result.append(temp | 0x80)
+        else:
+            result.append(temp)
+
+    return bytes(result)
+
+
+_cached_varuint_to_bytes = lru_cache(maxsize=1024)(_varuint_to_bytes)
+varuint_to_bytes = _cached_varuint_to_bytes
+
+
+def _bytes_to_varuint(value: _bytes) -> _int | None:
+    """Convert bytes to a varuint."""
+    result = 0
+    bitpos = 0
+    for val in value:
+        result |= (val & 0x7F) << bitpos
+        if (val & 0x80) == 0:
+            return result
+        bitpos += 7
+    return None
+
+
+_cached_bytes_to_varuint = lru_cache(maxsize=1024)(_bytes_to_varuint)
+bytes_to_varuint = _cached_bytes_to_varuint
+
 
 class APIPlaintextFrameHelper(APIFrameHelper):
     """Frame helper for plaintext API connections."""
diff --git a/aioesphomeapi/util.py b/aioesphomeapi/util.py
index 4d9c6d2..2f87f21 100644
--- a/aioesphomeapi/util.py
+++ b/aioesphomeapi/util.py
@@ -1,36 +1,6 @@
 from __future__ import annotations
 
 import math
-from functools import lru_cache
-
-
-@lru_cache(maxsize=1024)
-def varuint_to_bytes(value: int) -> bytes:
-    if value <= 0x7F:
-        return bytes([value])
-
-    ret = b""
-    while value:
-        temp = value & 0x7F
-        value >>= 7
-        if value:
-            ret += bytes([temp | 0x80])
-        else:
-            ret += bytes([temp])
-
-    return ret
-
-
-@lru_cache(maxsize=1024)
-def bytes_to_varuint(value: bytes) -> int | None:
-    result = 0
-    bitpos = 0
-    for val in value:
-        result |= (val & 0x7F) << bitpos
-        if (val & 0x80) == 0:
-            return result
-        bitpos += 7
-    return None
 
 
 def fix_float_single_double_conversion(value: float) -> float:
diff --git a/tests/test__frame_helper.py b/tests/test__frame_helper.py
index 6b2b25c..d333447 100644
--- a/tests/test__frame_helper.py
+++ b/tests/test__frame_helper.py
@@ -4,12 +4,19 @@ import pytest
 
 from aioesphomeapi._frame_helper import APINoiseFrameHelper, APIPlaintextFrameHelper
 from aioesphomeapi._frame_helper.base import WRITE_EXCEPTIONS
+from aioesphomeapi._frame_helper.plain_text import _bytes_to_varuint as bytes_to_varuint
+from aioesphomeapi._frame_helper.plain_text import (
+    _cached_bytes_to_varuint as cached_bytes_to_varuint,
+)
+from aioesphomeapi._frame_helper.plain_text import (
+    _cached_varuint_to_bytes as cached_varuint_to_bytes,
+)
+from aioesphomeapi._frame_helper.plain_text import _varuint_to_bytes as varuint_to_bytes
 from aioesphomeapi.core import (
     BadNameAPIError,
     InvalidEncryptionKeyAPIError,
     SocketAPIError,
 )
-from aioesphomeapi.util import varuint_to_bytes
 
 PREAMBLE = b"\x00"
 
@@ -234,3 +241,25 @@ async def test_noise_incorrect_name():
 
     with pytest.raises(BadNameAPIError):
         await helper.perform_handshake(30)
+
+
+VARUINT_TESTCASES = [
+    (0, b"\x00"),
+    (42, b"\x2a"),
+    (127, b"\x7f"),
+    (128, b"\x80\x01"),
+    (300, b"\xac\x02"),
+    (65536, b"\x80\x80\x04"),
+]
+
+
+@pytest.mark.parametrize("val, encoded", VARUINT_TESTCASES)
+def test_varuint_to_bytes(val, encoded):
+    assert varuint_to_bytes(val) == encoded
+    assert cached_varuint_to_bytes(val) == encoded
+
+
+@pytest.mark.parametrize("val, encoded", VARUINT_TESTCASES)
+def test_bytes_to_varuint(val, encoded):
+    assert bytes_to_varuint(encoded) == val
+    assert cached_bytes_to_varuint(encoded) == val
diff --git a/tests/test_util.py b/tests/test_util.py
index 897a9da..b4ba380 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -4,25 +4,6 @@ import pytest
 
 from aioesphomeapi import util
 
-VARUINT_TESTCASES = [
-    (0, b"\x00"),
-    (42, b"\x2a"),
-    (127, b"\x7f"),
-    (128, b"\x80\x01"),
-    (300, b"\xac\x02"),
-    (65536, b"\x80\x80\x04"),
-]
-
-
-@pytest.mark.parametrize("val, encoded", VARUINT_TESTCASES)
-def test_varuint_to_bytes(val, encoded):
-    assert util.varuint_to_bytes(val) == encoded
-
-
-@pytest.mark.parametrize("val, encoded", VARUINT_TESTCASES)
-def test_bytes_to_varuint(val, encoded):
-    assert util.bytes_to_varuint(encoded) == val
-
 
 @pytest.mark.parametrize(
     "input, output",