diff --git a/Lib/fontTools/ttLib/test/ttBrowser.py b/Lib/fontTools/ttLib/test/ttBrowser.py
index 1c5437594..67d0f7916 100644
--- a/Lib/fontTools/ttLib/test/ttBrowser.py
+++ b/Lib/fontTools/ttLib/test/ttBrowser.py
@@ -1,3 +1,5 @@
+"""Mac-only TrueType browser window."""
+
 from fontTools import ttLib
 from fontTools.ttLib import macUtils
 import macfs