diff --git a/piclib/built-in.scm b/piclib/built-in.scm
index 02b447fc..36e2ab29 100644
--- a/piclib/built-in.scm
+++ b/piclib/built-in.scm
@@ -1397,3 +1397,48 @@
 
 (import (picrin syntax-rules))
 (export syntax-rules)
+
+(define-library (scheme case-lambda)
+  (import (scheme base))
+
+  (define-syntax case-lambda
+    (syntax-rules ()
+      ((case-lambda
+        (?a1 ?e1 ...)
+        ?clause1 ...)
+       (lambda args
+         (let ((l (length args)))
+           (case-lambda "CLAUSE" args l
+                        (?a1 ?e1 ...)
+                        ?clause1 ...))))
+      ((case-lambda "CLAUSE" ?args ?l
+                    ((?a1 ...) ?e1 ...)
+                    ?clause1 ...)
+       (if (= ?l (length '(?a1 ...)))
+           (apply (lambda (?a1 ...) ?e1 ...) ?args)
+           (case-lambda "CLAUSE" ?args ?l
+                        ?clause1 ...)))
+      ((case-lambda "CLAUSE" ?args ?l
+                    ((?a1 . ?ar) ?e1 ...)
+                    ?clause1 ...)
+       (case-lambda "IMPROPER" ?args ?l 1 (?a1 . ?ar) (?ar ?e1 ...)
+                    ?clause1 ...))
+      ((case-lambda "CLAUSE" ?args ?l
+                    (?a1 ?e1 ...)
+                    ?clause1 ...)
+       (let ((?a1 ?args))
+         ?e1 ...))
+      ((case-lambda "CLAUSE" ?args ?l)
+       (error "Wrong number of arguments to CASE-LAMBDA."))
+      ((case-lambda "IMPROPER" ?args ?l ?k ?al ((?a1 . ?ar) ?e1 ...)
+                    ?clause1 ...)
+       (case-lambda "IMPROPER" ?args ?l (+ ?k 1) ?al (?ar ?e1 ...)
+                    ?clause1 ...))
+      ((case-lambda "IMPROPER" ?args ?l ?k ?al (?ar ?e1 ...)
+                    ?clause1 ...)
+       (if (>= ?l ?k)
+           (apply (lambda ?al ?e1 ...) ?args)
+           (case-lambda "CLAUSE" ?args ?l
+                        ?clause1 ...)))))
+
+  (export case-lambda))
diff --git a/t/r7rs-tests.scm b/t/r7rs-tests.scm
index ead83b4a..802d7dcc 100644
--- a/t/r7rs-tests.scm
+++ b/t/r7rs-tests.scm
@@ -36,8 +36,7 @@
         (scheme write)
 ;        (scheme eval)
         (scheme process-context)
-;        (scheme case-lambda)
-        )
+        (scheme case-lambda))
 
 ;; R7RS test suite.  Covers all procedures and syntax in the small
 ;; language except `delete-file'.  Currently assumes full-unicode
@@ -409,32 +408,32 @@
 (test '(list 3 4) (quasiquote (list (unquote (+ 1 2)) 4)) )
 (test `(list ,(+ 1 2) 4) (quasiquote (list (unquote (+ 1 2)) 4)))
 
-;; (define plus
-;;   (case-lambda
-;;    (() 0)
-;;    ((x) x)
-;;    ((x y) (+ x y))
-;;    ((x y z) (+ (+ x y) z))
-;;    (args (apply + args))))
+(define plus
+  (case-lambda
+   (() 0)
+   ((x) x)
+   ((x y) (+ x y))
+   ((x y z) (+ (+ x y) z))
+   (args (apply + args))))
 
-;; (test 0 (plus))
-;; (test 1 (plus 1))
-;; (test 3 (plus 1 2))
-;; (test 6 (plus 1 2 3))
-;; (test 10 (plus 1 2 3 4))
+(test 0 (plus))
+(test 1 (plus 1))
+(test 3 (plus 1 2))
+(test 6 (plus 1 2 3))
+(test 10 (plus 1 2 3 4))
 
-;; (define mult
-;;   (case-lambda
-;;    (() 1)
-;;    ((x) x)
-;;    ((x y) (* x y))
-;;    ((x y . z) (apply mult (* x y) z))))
+(define mult
+  (case-lambda
+   (() 1)
+   ((x) x)
+   ((x y) (* x y))
+   ((x y . z) (apply mult (* x y) z))))
 
-;; (test 1 (mult))
-;; (test 1 (mult 1))
-;; (test 2 (mult 1 2))
-;; (test 6 (mult 1 2 3))
-;; (test 24 (mult 1 2 3 4))
+(test 1 (mult))
+(test 1 (mult 1))
+(test 2 (mult 1 2))
+(test 6 (mult 1 2 3))
+(test 24 (mult 1 2 3 4))
 
 (test-end)