diff --git a/style_bert_vits2/constants.py b/style_bert_vits2/constants.py
index d5a46bf..5f32a15 100644
--- a/style_bert_vits2/constants.py
+++ b/style_bert_vits2/constants.py
@@ -1,6 +1,7 @@
-from enum import StrEnum
 from pathlib import Path
 
+from style_bert_vits2.utils.strenum import StrEnum
+
 
 # Style-Bert-VITS2 のバージョン
 LATEST_VERSION = "2.4"
diff --git a/style_bert_vits2/utils/strenum.py b/style_bert_vits2/utils/strenum.py
new file mode 100644
index 0000000..40d3b0c
--- /dev/null
+++ b/style_bert_vits2/utils/strenum.py
@@ -0,0 +1,36 @@
+import enum
+
+
+class StrEnum(str, enum.Enum):
+    """
+    Enum where members are also (and must be) strings (backported from Python 3.11).
+    """
+
+    def __new__(cls, *values: str) -> "StrEnum":
+        "values must already be of type `str`"
+        if len(values) > 3:
+            raise TypeError('too many arguments for str(): %r' % (values, ))
+        if len(values) == 1:
+            # it must be a string
+            if not isinstance(values[0], str):  # type: ignore
+                raise TypeError('%r is not a string' % (values[0], ))
+        if len(values) >= 2:
+            # check that encoding argument is a string
+            if not isinstance(values[1], str):  # type: ignore
+                raise TypeError('encoding must be a string, not %r' % (values[1], ))
+        if len(values) == 3:
+            # check that errors argument is a string
+            if not isinstance(values[2], str):  # type: ignore
+                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: list[str]) -> str:
+        """
+        Return the lower-cased version of the member name.
+        """
+        return name.lower()