diff --git a/homeassistant/helpers/service_info/dhcp.py b/homeassistant/helpers/service_info/dhcp.py
index d46c7a59004..94441749c65 100644
--- a/homeassistant/helpers/service_info/dhcp.py
+++ b/homeassistant/helpers/service_info/dhcp.py
@@ -18,3 +18,9 @@ class DhcpServiceInfo(BaseServiceInfo):
     as a lowercase string without colons.
     eg. "AA:BB:CC:12:34:56" is stored as "aabbcc123456"
     """
+
+    def __post_init__(self) -> None:
+        """Post-init processing."""
+        # Ensure macaddress is always a lowercase string without colons
+        if self.macaddress != self.macaddress.lower().replace(":", ""):
+            raise ValueError("macaddress is not correctly formatted")