diff --git a/arraycontext/container/arithmetic.py b/arraycontext/container/arithmetic.py
index 52c87d76800fb96b7070da68cf8a065a2d3f7b9a..9a6367009e3948444fb72e6282497443fd48ef89 100644
--- a/arraycontext/container/arithmetic.py
+++ b/arraycontext/container/arithmetic.py
@@ -41,6 +41,7 @@ import numpy as np
 T = TypeVar("T")
 
 
+@enum.unique
 class _OpClass(enum.Enum):
     ARITHMETIC = enum.auto()
     MATMUL = enum.auto()