diff --git a/src/init.c b/src/init.c
index 77c845d3..f189e6ff 100644
--- a/src/init.c
+++ b/src/init.c
@@ -1,5 +1,6 @@
 #include "picrin.h"
 
+void pic_init_pair(pic_state *);
 void pic_init_port(pic_state *);
 void pic_init_number(pic_state *);
 void pic_init_time(pic_state *);
@@ -14,6 +15,7 @@ pic_init_core(pic_state *pic)
   int ai;
 
   ai = pic_gc_arena_preserve(pic);
+  pic_init_pair(pic); DONE;
   pic_init_port(pic); DONE;
   pic_init_number(pic); DONE;
   pic_init_time(pic); DONE;
diff --git a/src/pair.c b/src/pair.c
index 9325cf22..bba2a181 100644
--- a/src/pair.c
+++ b/src/pair.c
@@ -82,3 +82,38 @@ pic_acons(pic_state *pic, pic_value key, pic_value val, pic_value assoc)
 {
   return pic_cons(pic, pic_cons(pic, key, val), assoc);
 }
+
+static pic_value
+pic_pair_set_car(pic_state *pic)
+{
+  pic_value v,w;
+
+  pic_get_args(pic, "oo", &v, &w);
+
+  if (! pic_pair_p(v))
+    pic_error(pic, "pair expected");
+
+  pic_pair_ptr(v)->car = w;
+  return pic_true_value();
+}
+
+static pic_value
+pic_pair_set_cdr(pic_state *pic)
+{
+  pic_value v,w;
+
+  pic_get_args(pic, "oo", &v, &w);
+
+  if (! pic_pair_p(v))
+    pic_error(pic, "pair expected");
+
+  pic_pair_ptr(v)->cdr = w;
+  return pic_true_value();
+}
+
+void
+pic_init_pair(pic_state *pic)
+{
+  pic_defun(pic, "set-car!", pic_pair_set_car);
+  pic_defun(pic, "set-cdr!", pic_pair_set_cdr);
+}