diff --git a/rwx/fs/__init__.py b/rwx/fs/__init__.py
index 82b7c16..a8865e7 100644
--- a/rwx/fs/__init__.py
+++ b/rwx/fs/__init__.py
@@ -58,8 +58,9 @@ def read_file_bytes(file_path: str) -> bytes:
         return file_object.read()
 
 
-def read_file_lines(file_path: str, charset: str = CHARSET):
-    return read_file_text(file_path).split(os.linesep)
+def read_file_lines(file_path: str, charset: str = CHARSET) -> list[str]:
+    """Read whole file lines."""
+    return read_file_text(file_path, charset).split(os.linesep)
 
 
 def read_file_text(file_path: str, charset: str = CHARSET) -> str: