diff --git a/abogen/domain/audio_sink.py b/abogen/domain/audio_sink.py
index 0fe9bd7..44cf939 100644
--- a/abogen/domain/audio_sink.py
+++ b/abogen/domain/audio_sink.py
@@ -54,7 +54,7 @@ def _ensure_ffmpeg() -> None:
 
 
 def _get_ffmpeg_cache_root() -> str:
-    from abogen.infrastructure.cache import get_internal_cache_path
+    from abogen.utils import get_internal_cache_path
 
     return get_internal_cache_path("ffmpeg")
 
diff --git a/abogen/domain/output_paths.py b/abogen/domain/output_paths.py
index 58c6f9a..4b79d40 100644
--- a/abogen/domain/output_paths.py
+++ b/abogen/domain/output_paths.py
@@ -76,7 +76,7 @@ def sanitize_filename_for_chapter(title: str, index: int, max_len: int = 80) ->
     return f"{index:02d}_{sanitized}"
 
 
-def sanitize_output_stem(name: str) -> str:
+def sanitize_output_stem(name: str, index: int = 0) -> str:
     base = Path(name or "").stem
     sanitized = _OUTPUT_SANITIZE_RE.sub("_", base).strip("_")
     return sanitized or "output"