diff --git a/homeassistant/components/microsoft/tts.py b/homeassistant/components/microsoft/tts.py
index bbfe9b0379e..1e1c088b351 100644
--- a/homeassistant/components/microsoft/tts.py
+++ b/homeassistant/components/microsoft/tts.py
@@ -54,6 +54,7 @@ SUPPORTED_LANGUAGES = [
     "ro-ro",
     "ru-ru",
     "sk-sk",
+    "sl-si",
     "sv-se",
     "th-th",
     "tr-tr",