diff --git a/rwx/cmd/squashfs/__init__.py b/rwx/cmd/squashfs/__init__.py
index 322186c..85e20b2 100644
--- a/rwx/cmd/squashfs/__init__.py
+++ b/rwx/cmd/squashfs/__init__.py
@@ -1,3 +1,5 @@
+"""Wrap SquashFS commands."""
+
 import ps
 
 import rwx.cmd
@@ -5,7 +7,8 @@ import rwx.cmd
 rwx.cmd.need("mksquashfs")
 
 
-def mksquashfs(input_root: str, output_file: str):
+def mksquashfs(input_root: str, output_file: str) -> None:
+    """Make a SquashFS bootable image file."""
     ps.run(
         [
             "mksquashfs",