diff --git a/include/picrin/port.h b/include/picrin/port.h
index 7604ed48..fbd0c884 100644
--- a/include/picrin/port.h
+++ b/include/picrin/port.h
@@ -41,4 +41,6 @@ struct pic_port *pic_stdin(pic_state *);
 struct pic_port *pic_stdout(pic_state *);
 struct pic_port *pic_stderr(pic_state *);
 
+pic_file *pic_funopen(void *cookie, int (*read)(void *, char *, int), int (*write)(void *, const char *, int), fpos_t (*seek)(void *, fpos_t, int), int (*close)(void *));
+
 #endif
diff --git a/src/port.c b/src/port.c
index a36af6a8..4586f18c 100644
--- a/src/port.c
+++ b/src/port.c
@@ -37,6 +37,28 @@ pic_stdout(pic_state *pic)
   return pic_port_ptr(pic_apply(pic, proc, pic_nil_value()));
 }
 
+pic_file *
+pic_funopen(void *cookie,
+            int (*read)(void *, char *, int),
+            int (*write)(void *, const char *, int),
+            fpos_t (*seek)(void *, fpos_t, int),
+            int (*close)(void *))
+{
+  pic_file *file;
+
+  file = (pic_file *)malloc(sizeof(pic_file));
+  if (! file) {
+    return NULL;
+  }
+  file->vtable.cookie = cookie;
+  file->vtable.read = read;
+  file->vtable.write = write;
+  file->vtable.seek = seek;
+  file->vtable.close = close;
+
+  return file;
+}
+
 static void write_pair(pic_state *pic, struct pic_pair *pair);
 static void write_str(pic_state *pic, struct pic_string *str);