diff --git a/doorcontrol/hid/Credential.py b/doorcontrol/hid/Credential.py
index 101cd12..fc10d92 100644
--- a/doorcontrol/hid/Credential.py
+++ b/doorcontrol/hid/Credential.py
@@ -21,7 +21,7 @@ class InvalidParity(InvalidHexCode):
         super().__init__(f"Bad {even_odd} parity")
 
 
-@dataclasses.dataclass
+@dataclasses.dataclass(frozen=True)
 class Credential:
     bits: bitstring.Bits