diff --git a/lib/scheme/char.sld b/lib/scheme/char.sld
index 604715a7..2da5c423 100644
--- a/lib/scheme/char.sld
+++ b/lib/scheme/char.sld
@@ -3,10 +3,12 @@
   (import (scheme base))
   (cond-expand
    (full-unicode
-    (import (chibi char-set full)
+    (import (scheme write)
+            (chibi char-set full)
             (chibi char-set base)
             (chibi iset base))
     (include "char/full.scm")
+    (include "char/special-casing.scm")
     (include "char/case-offsets.scm"))
    (else
     (include "char/ascii.scm")
diff --git a/lib/scheme/char/full.scm b/lib/scheme/char/full.scm
index 9a663b37..27b075ca 100644
--- a/lib/scheme/char/full.scm
+++ b/lib/scheme/char/full.scm
@@ -62,14 +62,40 @@
 (define (char-ci<=? a . ls) (char-cmp-ci <= a ls))
 (define (char-ci>=? a . ls) (char-cmp-ci >= a ls))
 
+(define (char-get-special-case ch off)
+  (let ((i (char->integer ch)))
+    (let loop ((a 0) (b (vector-length special-cases)))
+      (if (= a b)
+          #f
+          (let* ((mid (+ a (quotient (- b a) 2)))
+                 (vec (vector-ref special-cases mid))
+                 (val (vector-ref vec 0)))
+            (cond ((< i val) (if (= mid b) #f (loop a mid)))
+                  ((> i val) (if (= mid a) #f (loop mid b)))
+                  (else (vector-ref vec off))))))))
+
+(define (call-with-output-string proc)
+  (let ((out (open-output-string)))
+    (proc out)
+    (get-output-string out)))
+
 (define (string-downcase str)
-  (string-map char-downcase str))
+  (call-with-output-string
+    (lambda (out)
+      (string-for-each
+       (lambda (ch)
+         (display (or (char-get-special-case ch 1) (char-downcase ch)) out))
+       str))))
+
+(define string-foldcase string-downcase)
 
 (define (string-upcase str)
-  (string-map char-upcase str))
-
-(define (string-foldcase str)
-  (string-map char-foldcase str))
+  (call-with-output-string
+    (lambda (out)
+      (string-for-each
+       (lambda (ch)
+         (display (or (char-get-special-case ch 3) (char-upcase ch)) out))
+       str))))
 
 (define (string-cmp-ci op a ls)
   (let lp ((op op) (a (string-foldcase a)) (ls ls))
diff --git a/lib/scheme/char/special-casing.scm b/lib/scheme/char/special-casing.scm
new file mode 100644
index 00000000..83b32623
--- /dev/null
+++ b/lib/scheme/char/special-casing.scm
@@ -0,0 +1,109 @@
+
+;; Unconditoinal non-1-to-1 case mappings derived from Unicode data
+;; file SpecialCasing.txt.
+
+(define special-cases
+  ;; <code> <lower> <title> <upper>
+  #(#(223 "ß" "Ss" "SS")
+    #(304 "i̇" "İ" "İ")
+    #(329 "ʼn" "ʼN" "ʼN")
+    #(496 "ǰ" "J̌" "J̌")
+    #(912 "ΐ" "Ϊ́" "Ϊ́")
+    #(944 "ΰ" "Ϋ́" "Ϋ́")
+    #(1415 "և" "Եւ" "ԵՒ")
+    #(7830 "ẖ" "H̱" "H̱")
+    #(7831 "ẗ" "T̈" "T̈")
+    #(7832 "ẘ" "W̊" "W̊")
+    #(7833 "ẙ" "Y̊" "Y̊")
+    #(7834 "ẚ" "Aʾ" "Aʾ")
+    #(8016 "ὐ" "Υ̓" "Υ̓")
+    #(8018 "ὒ" "Υ̓̀" "Υ̓̀")
+    #(8020 "ὔ" "Υ̓́" "Υ̓́")
+    #(8022 "ὖ" "Υ̓͂" "Υ̓͂")
+    #(8064 "ᾀ" "ᾈ" "ἈΙ")
+    #(8065 "ᾁ" "ᾉ" "ἉΙ")
+    #(8066 "ᾂ" "ᾊ" "ἊΙ")
+    #(8067 "ᾃ" "ᾋ" "ἋΙ")
+    #(8068 "ᾄ" "ᾌ" "ἌΙ")
+    #(8069 "ᾅ" "ᾍ" "ἍΙ")
+    #(8070 "ᾆ" "ᾎ" "ἎΙ")
+    #(8071 "ᾇ" "ᾏ" "ἏΙ")
+    #(8072 "ᾀ" "ᾈ" "ἈΙ")
+    #(8073 "ᾁ" "ᾉ" "ἉΙ")
+    #(8074 "ᾂ" "ᾊ" "ἊΙ")
+    #(8075 "ᾃ" "ᾋ" "ἋΙ")
+    #(8076 "ᾄ" "ᾌ" "ἌΙ")
+    #(8077 "ᾅ" "ᾍ" "ἍΙ")
+    #(8078 "ᾆ" "ᾎ" "ἎΙ")
+    #(8079 "ᾇ" "ᾏ" "ἏΙ")
+    #(8080 "ᾐ" "ᾘ" "ἨΙ")
+    #(8081 "ᾑ" "ᾙ" "ἩΙ")
+    #(8082 "ᾒ" "ᾚ" "ἪΙ")
+    #(8083 "ᾓ" "ᾛ" "ἫΙ")
+    #(8084 "ᾔ" "ᾜ" "ἬΙ")
+    #(8085 "ᾕ" "ᾝ" "ἭΙ")
+    #(8086 "ᾖ" "ᾞ" "ἮΙ")
+    #(8087 "ᾗ" "ᾟ" "ἯΙ")
+    #(8088 "ᾐ" "ᾘ" "ἨΙ")
+    #(8089 "ᾑ" "ᾙ" "ἩΙ")
+    #(8090 "ᾒ" "ᾚ" "ἪΙ")
+    #(8091 "ᾓ" "ᾛ" "ἫΙ")
+    #(8092 "ᾔ" "ᾜ" "ἬΙ")
+    #(8093 "ᾕ" "ᾝ" "ἭΙ")
+    #(8094 "ᾖ" "ᾞ" "ἮΙ")
+    #(8095 "ᾗ" "ᾟ" "ἯΙ")
+    #(8096 "ᾠ" "ᾨ" "ὨΙ")
+    #(8097 "ᾡ" "ᾩ" "ὩΙ")
+    #(8098 "ᾢ" "ᾪ" "ὪΙ")
+    #(8099 "ᾣ" "ᾫ" "ὫΙ")
+    #(8100 "ᾤ" "ᾬ" "ὬΙ")
+    #(8101 "ᾥ" "ᾭ" "ὭΙ")
+    #(8102 "ᾦ" "ᾮ" "ὮΙ")
+    #(8103 "ᾧ" "ᾯ" "ὯΙ")
+    #(8104 "ᾠ" "ᾨ" "ὨΙ")
+    #(8105 "ᾡ" "ᾩ" "ὩΙ")
+    #(8106 "ᾢ" "ᾪ" "ὪΙ")
+    #(8107 "ᾣ" "ᾫ" "ὫΙ")
+    #(8108 "ᾤ" "ᾬ" "ὬΙ")
+    #(8109 "ᾥ" "ᾭ" "ὭΙ")
+    #(8110 "ᾦ" "ᾮ" "ὮΙ")
+    #(8111 "ᾧ" "ᾯ" "ὯΙ")
+    #(8114 "ᾲ" "Ὰͅ" "ᾺΙ")
+    #(8115 "ᾳ" "ᾼ" "ΑΙ")
+    #(8116 "ᾴ" "Άͅ" "ΆΙ")
+    #(8118 "ᾶ" "Α͂" "Α͂")
+    #(8119 "ᾷ" "ᾼ͂" "Α͂Ι")
+    #(8124 "ᾳ" "ᾼ" "ΑΙ")
+    #(8130 "ῂ" "Ὴͅ" "ῊΙ")
+    #(8131 "ῃ" "ῌ" "ΗΙ")
+    #(8132 "ῄ" "Ήͅ" "ΉΙ")
+    #(8134 "ῆ" "Η͂" "Η͂")
+    #(8135 "ῇ" "ῌ͂" "Η͂Ι")
+    #(8140 "ῃ" "ῌ" "ΗΙ")
+    #(8146 "ῒ" "Ϊ̀" "Ϊ̀")
+    #(8147 "ΐ" "Ϊ́" "Ϊ́")
+    #(8150 "ῖ" "Ι͂" "Ι͂")
+    #(8151 "ῗ" "Ϊ͂" "Ϊ͂")
+    #(8162 "ῢ" "Ϋ̀" "Ϋ̀")
+    #(8163 "ΰ" "Ϋ́" "Ϋ́")
+    #(8164 "ῤ" "Ρ̓" "Ρ̓")
+    #(8166 "ῦ" "Υ͂" "Υ͂")
+    #(8167 "ῧ" "Ϋ͂" "Ϋ͂")
+    #(8178 "ῲ" "Ὼͅ" "ῺΙ")
+    #(8179 "ῳ" "ῼ" "ΩΙ")
+    #(8180 "ῴ" "Ώͅ" "ΏΙ")
+    #(8182 "ῶ" "Ω͂" "Ω͂")
+    #(8183 "ῷ" "ῼ͂" "Ω͂Ι")
+    #(8188 "ῳ" "ῼ" "ΩΙ")
+    #(64256 "ff" "Ff" "FF")
+    #(64257 "fi" "Fi" "FI")
+    #(64258 "fl" "Fl" "FL")
+    #(64259 "ffi" "Ffi" "FFI")
+    #(64260 "ffl" "Ffl" "FFL")
+    #(64261 "ſt" "St" "ST")
+    #(64262 "st" "St" "ST")
+    #(64275 "ﬓ" "Մն" "ՄՆ")
+    #(64276 "ﬔ" "Մե" "ՄԵ")
+    #(64277 "ﬕ" "Մի" "ՄԻ")
+    #(64278 "ﬖ" "Վն" "ՎՆ")
+    #(64279 "ﬗ" "Մխ" "ՄԽ")))
diff --git a/tests/r7rs-tests.scm b/tests/r7rs-tests.scm
index 3782dbcb..5050b2ca 100644
--- a/tests/r7rs-tests.scm
+++ b/tests/r7rs-tests.scm
@@ -1103,6 +1103,7 @@
 (test #t (string-ci<=? "ΑΒΓ" "αβγ"))
 (test #t (string-ci>=? "ΑΒΓ" "αβγ"))
 
+;; latin
 (test "ABC" (string-upcase "abc"))
 (test "ABC" (string-upcase "ABC"))
 (test "abc" (string-downcase "abc"))
@@ -1110,6 +1111,7 @@
 (test "abc" (string-foldcase "abc"))
 (test "abc" (string-foldcase "ABC"))
 
+;; cyrillic
 (test "ΑΒΓ" (string-upcase "αβγ"))
 (test "ΑΒΓ" (string-upcase "ΑΒΓ"))
 (test "αβγ" (string-downcase "αβγ"))
@@ -1117,6 +1119,15 @@
 (test "αβγ" (string-foldcase "αβγ"))
 (test "αβγ" (string-foldcase "ΑΒΓ"))
 
+;; special cases
+(test "SSA" (string-upcase "ßa"))
+(test "ßa" (string-downcase "ßa"))
+(test "ssa" (string-downcase "SSA"))
+(test "İ" (string-upcase "İ"))
+(test "i̇" (string-downcase "İ"))
+(test "i̇" (string-foldcase "İ"))
+(test "J̌" (string-upcase "ǰ"))
+
 (test "" (substring "" 0 0))
 (test "" (substring "a" 0 0))
 (test "" (substring "abc" 1 1))