diff --git a/tests/conftest.py b/tests/conftest.py
index 130ce74dd5b..a07e659378a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -99,6 +99,7 @@ from homeassistant.helpers import (
     translation as translation_helper,
 )
 from homeassistant.helpers.dispatcher import async_dispatcher_send
+from homeassistant.helpers.service_info.dhcp import DhcpServiceInfo
 from homeassistant.helpers.translation import _TranslationsCacheData
 from homeassistant.helpers.typing import ConfigType
 from homeassistant.setup import async_setup_component
@@ -2090,3 +2091,21 @@ def disable_block_async_io() -> Generator[None]:
             blocking_call.object, blocking_call.function, blocking_call.original_func
         )
     calls.clear()
+
+
+# Ensure that incorrectly formatted mac addresses are rejected during
+# DhcpServiceInfo initialisation
+_real_dhcp_service_info_init = DhcpServiceInfo.__init__
+
+
+def _dhcp_service_info_init(self: DhcpServiceInfo, *args: Any, **kwargs: Any) -> None:
+    """Override __init__ for DhcpServiceInfo.
+
+    Ensure that the macaddress is always in lowercase and without colons to match DHCP service.
+    """
+    _real_dhcp_service_info_init(self, *args, **kwargs)
+    if self.macaddress != self.macaddress.lower().replace(":", ""):
+        raise ValueError("macaddress is not correctly formatted")
+
+
+DhcpServiceInfo.__init__ = _dhcp_service_info_init
diff --git a/tests/helpers/test_service_info.py b/tests/helpers/test_service_info.py
new file mode 100644
index 00000000000..249ceb0e637
--- /dev/null
+++ b/tests/helpers/test_service_info.py
@@ -0,0 +1,23 @@
+"""Test service_info helpers."""
+
+import pytest
+
+from homeassistant.helpers.service_info.dhcp import DhcpServiceInfo
+
+# Ensure that incorrectly formatted mac addresses are rejected, even
+# on a constant outside of a test
+try:
+    _ = DhcpServiceInfo(ip="", hostname="", macaddress="AA:BB:CC:DD:EE:FF")
+except ValueError:
+    pass
+else:
+    raise RuntimeError(
+        "DhcpServiceInfo incorrectly formatted mac address was not rejected. "
+        "Please ensure that the DhcpServiceInfo is correctly patched."
+    )
+
+
+def test_invalid_macaddress() -> None:
+    """Test that DhcpServiceInfo raises ValueError for unformatted macaddress."""
+    with pytest.raises(ValueError):
+        DhcpServiceInfo(ip="", hostname="", macaddress="AA:BB:CC:DD:EE:FF")