diff --git a/src/packaging/specifiers.py b/src/packaging/specifiers.py
index e1874327..3466c793 100644
--- a/src/packaging/specifiers.py
+++ b/src/packaging/specifiers.py
@@ -49,7 +49,7 @@ class InvalidSpecifier(ValueError):
     """
 
 
-class BaseSpecifier(metaclass=abc.ABCMeta):
+class BaseSpecifier(abc.ABC):
     @abc.abstractmethod
     def __str__(self) -> str:
         """