diff --git a/TTS/tts/utils/text/characters.py b/TTS/tts/utils/text/characters.py
index 0ce65a90..f6c04370 100644
--- a/TTS/tts/utils/text/characters.py
+++ b/TTS/tts/utils/text/characters.py
@@ -1,3 +1,4 @@
+from abc import ABC
 from dataclasses import replace
 from typing import Dict