diff --git a/include/picrin.h b/include/picrin.h
index 8719b79e..37830c1a 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -143,15 +143,13 @@ void pic_close(pic_state *);
 
 void pic_add_feature(pic_state *, const char *);
 
-void pic_define(pic_state *, const char *, pic_value); /* automatic export */
 bool pic_defined_p(pic_state *, struct pic_lib *, const char *);
-pic_value pic_ref(pic_state *, struct pic_lib *, const char *);
-void pic_set(pic_state *, struct pic_lib *, const char *, pic_value);
-pic_value pic_funcall(pic_state *pic, const char *name, pic_list args);
+void pic_define(pic_state *, const char *, pic_value); /* automatic export */
+void pic_defun(pic_state *, const char *, pic_func_t);
+void pic_defvar(pic_state *, const char *, pic_value, struct pic_proc *);
 
 struct pic_proc *pic_get_proc(pic_state *);
 int pic_get_args(pic_state *, const char *, ...);
-void pic_defun(pic_state *, const char *, pic_func_t);
 
 bool pic_equal_p(pic_state *, pic_value, pic_value);
 
@@ -172,6 +170,10 @@ pic_value pic_read_cstr(pic_state *, const char *);
 void pic_load(pic_state *, const char *);
 void pic_load_cstr(pic_state *, const char *);
 
+pic_value pic_funcall(pic_state *pic, const char *, pic_list);
+pic_value pic_ref(pic_state *, struct pic_lib *, const char *);
+void pic_set(pic_state *, struct pic_lib *, const char *, pic_value);
+
 pic_value pic_apply(pic_state *, struct pic_proc *, pic_value);
 pic_value pic_apply0(pic_state *, struct pic_proc *);
 pic_value pic_apply1(pic_state *, struct pic_proc *, pic_value);
diff --git a/port.c b/port.c
index 6b27040d..11ef26ab 100644
--- a/port.c
+++ b/port.c
@@ -681,9 +681,9 @@ pic_port_flush(pic_state *pic)
 void
 pic_init_port(pic_state *pic)
 {
-  pic_define(pic, "current-input-port", pic_obj_value(pic_make_var(pic, pic_obj_value(pic->xSTDIN), NULL)));
-  pic_define(pic, "current-output-port", pic_obj_value(pic_make_var(pic, pic_obj_value(pic->xSTDOUT), NULL)));
-  pic_define(pic, "current-error-port", pic_obj_value(pic_make_var(pic, pic_obj_value(pic->xSTDERR), NULL)));
+  pic_defvar(pic, "current-input-port", pic_obj_value(pic->xSTDIN), NULL);
+  pic_defvar(pic, "current-output-port", pic_obj_value(pic->xSTDOUT), NULL);
+  pic_defvar(pic, "current-error-port", pic_obj_value(pic->xSTDERR), NULL);
 
   pic_defun(pic, "call-with-port", pic_port_call_with_port);
 
diff --git a/vm.c b/vm.c
index 05ddda7c..d2270ccb 100644
--- a/vm.c
+++ b/vm.c
@@ -479,6 +479,12 @@ pic_defun(pic_state *pic, const char *name, pic_func_t cfunc)
   pic_define(pic, name, pic_obj_value(proc));
 }
 
+void
+pic_defvar(pic_state *pic, const char *name, pic_value init, struct pic_proc *conv)
+{
+  pic_define(pic, name, pic_obj_value(pic_make_var(pic, init, conv)));
+}
+
 static void
 vm_push_env(pic_state *pic)
 {