diff --git a/src/mbyte.c b/src/mbyte.c
index 2394401..ca3204f 100644
--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -2949,7 +2949,7 @@
 {
 	{0x61,0x7a,1,-32},
 	{0xb5,0xb5,-1,743},
-	{0xe0,0xf6,1,-32},
+	{0xe0,0xf6,1,-32},  /* 0xdf (German sharp s) is not upper-cased */
 	{0xf8,0xfe,1,-32},
 	{0xff,0xff,-1,121},
 	{0x101,0x12f,2,-1},
@@ -3129,7 +3129,8 @@
 utf_islower(a)
     int		a;
 {
-    return (utf_toupper(a) != a);
+    /* German sharp s is lower case but has no upper case equivalent. */
+    return (utf_toupper(a) != a) || a == 0xdf;
 }
 
 /*