diff --git a/comicapi/merge.py b/comicapi/merge.py
index 2c6c4f6..8e3a724 100644
--- a/comicapi/merge.py
+++ b/comicapi/merge.py
@@ -1,51 +1,12 @@
 from __future__ import annotations
 
 import dataclasses
-import sys
 from collections import defaultdict
 from collections.abc import Collection
-from enum import Enum, auto
+from enum import auto
 from typing import Any
 
-from comicapi.utils import norm_fold
-
-if sys.version_info < (3, 11):
-
-    class StrEnum(str, Enum):
-        """
-        Enum where members are also (and must be) strings
-        """
-
-        def __new__(cls, *values: Any) -> Any:
-            "values must already be of type `str`"
-            if len(values) > 3:
-                raise TypeError(f"too many arguments for str(): {values!r}")
-            if len(values) == 1:
-                # it must be a string
-                if not isinstance(values[0], str):
-                    raise TypeError(f"{values[0]!r} is not a string")
-            if len(values) >= 2:
-                # check that encoding argument is a string
-                if not isinstance(values[1], str):
-                    raise TypeError(f"encoding must be a string, not {values[1]!r}")
-            if len(values) == 3:
-                # check that errors argument is a string
-                if not isinstance(values[2], str):
-                    raise TypeError("errors must be a string, not %r" % (values[2]))
-            value = str(*values)
-            member = str.__new__(cls, value)
-            member._value_ = value
-            return member
-
-        @staticmethod
-        def _generate_next_value_(name: str, start: int, count: int, last_values: Any) -> str:
-            """
-            Return the lower-cased version of the member name.
-            """
-            return name.lower()
-
-else:
-    from enum import StrEnum
+from comicapi.utils import StrEnum, norm_fold
 
 
 @dataclasses.dataclass
diff --git a/comicapi/utils.py b/comicapi/utils.py
index dac74bc..a7165b8 100644
--- a/comicapi/utils.py
+++ b/comicapi/utils.py
@@ -82,8 +82,28 @@ if sys.version_info < (3, 11):
             """
             return name.lower()
 
+        @classmethod
+        def _missing_(cls, value: Any) -> str | None:
+            if not isinstance(value, str):
+                return None
+            if not hasattr(cls, "_lower_members"):
+                cls._lower_members = {x.casefold(): x for x in cls}  # type: ignore[attr-defined]
+            return cls._lower_members.get(value.casefold(), None)  # type: ignore[attr-defined]
+
+        def __str__(self):
+            return self.value
+
 else:
-    from enum import StrEnum
+    from enum import StrEnum as s
+
+    class StrEnum(s):
+        @classmethod
+        def _missing_(cls, value: Any) -> str | None:
+            if not isinstance(value, str):
+                return None
+            if not hasattr(cls, "_lower_members"):
+                cls._lower_members = {x.casefold(): x for x in cls}  # type: ignore[attr-defined]
+            return cls._lower_members.get(value.casefold(), None)  # type: ignore[attr-defined]
 
 
 logger = logging.getLogger(__name__)