diff --git a/lib/init-7.scm b/lib/init-7.scm
index aae56127..4277aa78 100644
--- a/lib/init-7.scm
+++ b/lib/init-7.scm
@@ -369,11 +369,6 @@
   (if (<= n 9)
       (integer->char (+ n (char->integer #\0)))
       (integer->char (+ (- n 10) (char->integer #\A)))))
-(define (digit-value ch)
-  (if (char-numeric? ch)
-      (- (char->integer ch) (char->integer #\0))
-      (and (<= 65 (char->integer (char-upcase ch)) 70)
-           (- (char->integer (char-upcase ch)) 55))))
 
 (define (%number->string num)
   (call-with-output-string (lambda (out) (write num out))))
diff --git a/lib/scheme/char.sld b/lib/scheme/char.sld
index eae10fd1..604715a7 100644
--- a/lib/scheme/char.sld
+++ b/lib/scheme/char.sld
@@ -5,8 +5,7 @@
    (full-unicode
     (import (chibi char-set full)
             (chibi char-set base)
-            (chibi iset base)
-            (only (chibi) digit-value))
+            (chibi iset base))
     (include "char/full.scm")
     (include "char/case-offsets.scm"))
    (else
@@ -18,6 +17,7 @@
            char-alphabetic?  char-lower-case? char-numeric?
            char-upper-case? char-whitespace? digit-value
            char-upcase char-downcase))))
+  (include "digit-value.scm")
   (export
    char-alphabetic? char-ci<=? char-ci<? char-ci=? char-ci>=? char-ci>?
    char-downcase char-foldcase char-lower-case? char-numeric?
diff --git a/lib/scheme/digit-value.scm b/lib/scheme/digit-value.scm
new file mode 100644
index 00000000..c09cf010
--- /dev/null
+++ b/lib/scheme/digit-value.scm
@@ -0,0 +1,64 @@
+
+(cond-expand
+ (full-unicode
+  (define zeros
+    '#(#\x0030                ;DIGIT ZERO
+       #\x0660                ;ARABIC-INDIC DIGIT ZERO
+       #\x06F0                ;EXTENDED ARABIC-INDIC DIGIT ZERO
+       #\x07C0                ;NKO DIGIT ZERO
+       #\x0966                ;DEVANAGARI DIGIT ZERO
+       #\x09E6                ;BENGALI DIGIT ZERO
+       #\x0A66                ;GURMUKHI DIGIT ZERO
+       #\x0AE6                ;GUJARATI DIGIT ZERO
+       #\x0B66                ;ORIYA DIGIT ZERO
+       #\x0BE6                ;TAMIL DIGIT ZERO
+       #\x0C66                ;TELUGU DIGIT ZERO
+       #\x0CE6                ;KANNADA DIGIT ZERO
+       #\x0D66                ;MALAYALAM DIGIT ZERO
+       #\x0E50                ;THAI DIGIT ZERO
+       #\x0ED0                ;LAO DIGIT ZERO
+       #\x0F20                ;TIBETAN DIGIT ZERO
+       #\x1040                ;MYANMAR DIGIT ZERO
+       #\x1090                ;MYANMAR SHAN DIGIT ZERO
+       #\x17E0                ;KHMER DIGIT ZERO
+       #\x1810                ;MONGOLIAN DIGIT ZERO
+       #\x1946                ;LIMBU DIGIT ZERO
+       #\x19D0                ;NEW TAI LUE DIGIT ZERO
+       #\x1A80                ;TAI THAM HORA DIGIT ZERO
+       #\x1A90                ;TAI THAM THAM DIGIT ZERO
+       #\x1B50                ;BALINESE DIGIT ZERO
+       #\x1BB0                ;SUNDANESE DIGIT ZERO
+       #\x1C40                ;LEPCHA DIGIT ZERO
+       #\x1C50                ;OL CHIKI DIGIT ZERO
+       #\xA620                ;VAI DIGIT ZERO
+       #\xA8D0                ;SAURASHTRA DIGIT ZERO
+       #\xA900                ;KAYAH LI DIGIT ZERO
+       #\xA9D0                ;JAVANESE DIGIT ZERO
+       #\xAA50                ;CHAM DIGIT ZERO
+       #\xABF0                ;MEETEI MAYEK DIGIT ZERO
+       #\xFF10                ;FULLWIDTH DIGIT ZERO
+       #\x104A0               ;OSMANYA DIGIT ZERO
+       #\x11066               ;BRAHMI DIGIT ZERO
+       #\x1D7CE               ;MATHEMATICAL BOLD DIGIT ZERO
+       #\x1D7D8               ;MATHEMATICAL DOUBLE-STRUCK DIGIT ZERO
+       #\x1D7E2               ;MATHEMATICAL SANS-SERIF DIGIT ZERO
+       #\x1D7EC               ;MATHEMATICAL SANS-SERIF BOLD DIGIT ZERO
+       #\x1D7F6               ;MATHEMATICAL MONOSPACE DIGIT ZERO
+       )))
+ (else
+  (define zeros #(#\0))))
+
+(define (digit-value ch)
+  (let ((n (char->integer ch)))
+    (let lp ((lo 0) (hi (- (vector-length zeros) 1)))
+      (if (> lo hi)
+          #f
+          (let* ((mid (+ lo (quotient (- hi lo) 2)))
+                 (mid-zero (char->integer (vector-ref zeros mid))))
+            (cond
+             ((<= mid-zero n (+ mid-zero 9))
+              (- n mid-zero))
+             ((< n mid-zero)
+              (lp lo (- mid 1)))
+             (else
+              (lp (+ mid 1) hi))))))))
diff --git a/tests/r7rs-tests.scm b/tests/r7rs-tests.scm
index bf560f33..9f0a12f5 100644
--- a/tests/r7rs-tests.scm
+++ b/tests/r7rs-tests.scm
@@ -855,9 +855,13 @@
 (test #f (char-lower-case? #\A))
 (test #f (char-lower-case? #\3))
 
+(test 0 (digit-value #\0))
 (test 3 (digit-value #\3))
-;; (test 4 (digit-value #\x0664))
-;; (test 0 (digit-value #\x0EA6))
+(test 9 (digit-value #\9))
+(test 4 (digit-value #\x0664))
+(test 0 (digit-value #\x0AE6))
+(test #f (digit-value #\.))
+(test #f (digit-value #\-))
 
 (test 97 (char->integer #\a))
 (test #\a (integer->char 97))
@@ -1468,7 +1472,7 @@
 
 ;; Each test is of the form:
 ;;
-;;   (input-str expected-value (expected-write-values ...))
+;;   (input-str expected-value expected-write-values ...)
 ;;
 ;; where the input should be eqv? to the expected-value, and the
 ;; written output the same as any of the expected-write-values.  The