diff --git a/include/picrin/pair.h b/include/picrin/pair.h
index 64d5d1cb..1f7fccfa 100644
--- a/include/picrin/pair.h
+++ b/include/picrin/pair.h
@@ -21,6 +21,8 @@ struct pic_pair {
 pic_value pic_cons(pic_state *, pic_value, pic_value);
 pic_value pic_car(pic_state *, pic_value);
 pic_value pic_cdr(pic_state *, pic_value);
+void pic_set_car(pic_state *, pic_value, pic_value);
+void pic_set_cdr(pic_state *, pic_value, pic_value);
 
 bool pic_list_p(pic_value);
 pic_value pic_list1(pic_state *, pic_value);
diff --git a/src/pair.c b/src/pair.c
index bb4ef0bb..499b7bb5 100644
--- a/src/pair.c
+++ b/src/pair.c
@@ -45,6 +45,32 @@ pic_cdr(pic_state *pic, pic_value obj)
   return pair->cdr;
 }
 
+void
+pic_set_car(pic_state *pic, pic_value obj, pic_value val)
+{
+  struct pic_pair *pair;
+
+  if (! pic_pair_p(obj)) {
+    pic_error(pic, "pair required");
+  }
+  pair = pic_pair_ptr(obj);
+
+  pair->car = val;
+}
+
+void
+pic_set_cdr(pic_state *pic, pic_value obj, pic_value val)
+{
+  struct pic_pair *pair;
+
+  if (! pic_pair_p(obj)) {
+    pic_error(pic, "pair required");
+  }
+  pair = pic_pair_ptr(obj);
+
+  pair->cdr = val;
+}
+
 bool
 pic_list_p(pic_value obj)
 {