diff --git a/src/mbyte.c b/src/mbyte.c
index 2d18a27..0427f0c 100644
--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -3454,6 +3454,8 @@
 	{0x1e900,0x1e921,1,34}
 };
 
+// Note: UnicodeData.txt does not define U+1E9E as being the corresponding upper
+// case letter for U+00DF (ß), however it is part of the toLower table
 static convertStruct toUpper[] =
 {
 	{0x61,0x7a,1,-32},