diff --git a/contrib/05.r7rs/src/file.c b/contrib/05.r7rs/src/file.c
index ce9cb1b2..36e50e86 100644
--- a/contrib/05.r7rs/src/file.c
+++ b/contrib/05.r7rs/src/file.c
@@ -27,8 +27,7 @@ generic_open_file(pic_state *pic, const char *fname, char *mode, short flags)
 
   port = (struct pic_port *)pic_obj_alloc(pic, sizeof(struct pic_port), PIC_TT_PORT);
   port->file = file;
-  port->flags = flags;
-  port->status = PIC_PORT_OPEN;
+  port->flags = flags | PIC_PORT_OPEN;
 
   return pic_obj_value(port);
 }
diff --git a/contrib/05.r7rs/src/load.c b/contrib/05.r7rs/src/load.c
index c887a1b2..385767d8 100644
--- a/contrib/05.r7rs/src/load.c
+++ b/contrib/05.r7rs/src/load.c
@@ -17,8 +17,7 @@ pic_load(pic_state *pic, const char *filename)
 
   port = (struct pic_port *)pic_obj_alloc(pic, sizeof(struct pic_port), PIC_TT_PORT);
   port->file = file;
-  port->flags = PIC_PORT_IN | PIC_PORT_TEXT;
-  port->status = PIC_PORT_OPEN;
+  port->flags = PIC_PORT_IN | PIC_PORT_TEXT | PIC_PORT_OPEN;
 
   pic_load_port(pic, port);
 
diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index 5ed749b7..59ea6850 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -617,17 +617,6 @@ gc_mark_phase(pic_state *pic)
   /* library table */
   gc_mark(pic, pic->libs);
 
-  /* standard I/O ports */
-  if (pic->xSTDIN) {
-    gc_mark_object(pic, (struct pic_object *)pic->xSTDIN);
-  }
-  if (pic->xSTDOUT) {
-    gc_mark_object(pic, (struct pic_object *)pic->xSTDOUT);
-  }
-  if (pic->xSTDERR) {
-    gc_mark_object(pic, (struct pic_object *)pic->xSTDERR);
-  }
-
   /* parameter table */
   gc_mark(pic, pic->ptable);
 
diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index a063fa68..d0dedfa5 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -143,12 +143,9 @@ typedef struct {
   size_t arena_size, arena_idx;
   struct pic_reg *regs;
 
-  struct pic_port *xSTDIN, *xSTDOUT, *xSTDERR;
-
   pic_value err;
 
   pic_code *iseq;               /* for pic_apply_trampoline */
-
   char *native_stack_start;
 } pic_state;
 
@@ -204,6 +201,10 @@ void pic_load_port(pic_state *, struct pic_port *);
 void pic_load_cstr(pic_state *, const char *);
 
 pic_value pic_funcall(pic_state *pic, struct pic_lib *, const char *, pic_list);
+pic_value pic_funcall0(pic_state *pic, struct pic_lib *, const char *);
+pic_value pic_funcall1(pic_state *pic, struct pic_lib *, const char *, pic_value);
+pic_value pic_funcall2(pic_state *pic, struct pic_lib *, const char *, pic_value, pic_value);
+pic_value pic_funcall3(pic_state *pic, struct pic_lib *, const char *, pic_value, pic_value, pic_value);
 pic_value pic_ref(pic_state *, struct pic_lib *, const char *);
 void pic_set(pic_state *, struct pic_lib *, const char *, pic_value);
 
@@ -257,7 +258,7 @@ pic_value pic_display(pic_state *, pic_value);
 pic_value pic_fdisplay(pic_state *, pic_value, xFILE *);
 
 #if DEBUG
-# define pic_debug(pic,obj) pic_fwrite(pic,obj,pic->xSTDERR->file)
+# define pic_debug(pic,obj) pic_fwrite(pic,obj,xstderr)
 # define pic_fdebug(pic,obj,file) pic_fwrite(pic,obj,file)
 #endif
 
diff --git a/extlib/benz/include/picrin/port.h b/extlib/benz/include/picrin/port.h
index 98dcff83..dfb664e6 100644
--- a/extlib/benz/include/picrin/port.h
+++ b/extlib/benz/include/picrin/port.h
@@ -13,19 +13,14 @@ enum pic_port_flag {
   PIC_PORT_IN = 1,
   PIC_PORT_OUT = 2,
   PIC_PORT_TEXT = 4,
-  PIC_PORT_BINARY = 8
-};
-
-enum pic_port_status {
-  PIC_PORT_OPEN,
-  PIC_PORT_CLOSE
+  PIC_PORT_BINARY = 8,
+  PIC_PORT_OPEN = 16
 };
 
 struct pic_port {
   PIC_OBJECT_HEADER
   xFILE *file;
   int flags;
-  int status;
 };
 
 #define pic_port_p(v) (pic_type(v) == PIC_TT_PORT)
diff --git a/extlib/benz/port.c b/extlib/benz/port.c
index 5b04f89b..c73cabd5 100644
--- a/extlib/benz/port.c
+++ b/extlib/benz/port.c
@@ -14,48 +14,45 @@ pic_eof_object()
   return v;
 }
 
-struct pic_port *
-pic_stdin(pic_state *pic)
+static pic_value
+pic_assert_port(pic_state *pic)
 {
-  pic_value obj;
+  struct pic_port *port;
 
-  obj = pic_funcall(pic, pic->PICRIN_BASE, "current-input-port", pic_nil_value());
+  pic_get_args(pic, "p", &port);
 
-  return pic_port_ptr(obj);
+  return pic_obj_value(port);
 }
 
-struct pic_port *
-pic_stdout(pic_state *pic)
-{
-  pic_value obj;
+/* current-(input|output|error)-port */
 
-  obj = pic_funcall(pic, pic->PICRIN_BASE, "current-output-port", pic_nil_value());
-
-  return pic_port_ptr(obj);
-}
-
-struct pic_port *
-pic_stderr(pic_state *pic)
-{
-  pic_value obj;
-
-  obj = pic_funcall(pic, pic->PICRIN_BASE, "current-error-port", pic_nil_value());
-
-  return pic_port_ptr(obj);
-}
-
-struct pic_port *
-pic_make_standard_port(pic_state *pic, xFILE *file, short dir)
+static void
+pic_define_standard_port(pic_state *pic, const char *name, xFILE *file, int dir)
 {
   struct pic_port *port;
 
   port = (struct pic_port *)pic_obj_alloc(pic, sizeof(struct pic_port), PIC_TT_PORT);
   port->file = file;
-  port->flags = dir | PIC_PORT_TEXT;
-  port->status = PIC_PORT_OPEN;
-  return port;
+  port->flags = dir | PIC_PORT_TEXT | PIC_PORT_OPEN;
+
+  pic_defvar(pic, name, pic_obj_value(port), pic_make_proc(pic, pic_assert_port, "pic_assert_port"));
 }
 
+#define DEFINE_STANDARD_PORT_ACCESSOR(name, var)        \
+  struct pic_port *                                     \
+  name(pic_state *pic)                                  \
+  {                                                     \
+    pic_value obj;                                      \
+                                                        \
+    obj = pic_funcall0(pic, pic->PICRIN_BASE, var);     \
+                                                        \
+    return pic_port_ptr(obj);                           \
+  }
+
+DEFINE_STANDARD_PORT_ACCESSOR(pic_stdin, "current-input-port")
+DEFINE_STANDARD_PORT_ACCESSOR(pic_stdout, "current-output-port")
+DEFINE_STANDARD_PORT_ACCESSOR(pic_stderr, "current-error-port")
+
 struct strfile {
   pic_state *pic;
   char *buf;
@@ -155,8 +152,7 @@ pic_open_input_string(pic_state *pic, const char *str)
 
   port = (struct pic_port *)pic_obj_alloc(pic, sizeof(struct pic_port *), PIC_TT_PORT);
   port->file = string_open(pic, str, strlen(str));
-  port->flags = PIC_PORT_IN | PIC_PORT_TEXT;
-  port->status = PIC_PORT_OPEN;
+  port->flags = PIC_PORT_IN | PIC_PORT_TEXT | PIC_PORT_OPEN;
 
   return port;
 }
@@ -168,8 +164,7 @@ pic_open_output_string(pic_state *pic)
 
   port = (struct pic_port *)pic_obj_alloc(pic, sizeof(struct pic_port *), PIC_TT_PORT);
   port->file = string_open(pic, NULL, 0);
-  port->flags = PIC_PORT_OUT | PIC_PORT_TEXT;
-  port->status = PIC_PORT_OPEN;
+  port->flags = PIC_PORT_OUT | PIC_PORT_TEXT | PIC_PORT_OPEN;
 
   return port;
 }
@@ -196,7 +191,7 @@ pic_close_port(pic_state *pic, struct pic_port *port)
   if (xfclose(port->file) == EOF) {
     pic_errorf(pic, "close-port: failure");
   }
-  port->status = PIC_PORT_CLOSE;
+  port->flags &= ~PIC_PORT_OPEN;
 }
 
 static pic_value
@@ -315,7 +310,7 @@ pic_port_port_open_p(pic_state *pic)
 
   pic_get_args(pic, "p", &port);
 
-  return pic_bool_value(port->status == PIC_PORT_OPEN);
+  return pic_bool_value(port->flags & PIC_PORT_OPEN);
 }
 
 static pic_value
@@ -330,7 +325,7 @@ pic_port_close_port(pic_state *pic)
   return pic_undef_value();
 }
 
-#define assert_port_profile(port, flgs, stat, caller) do {              \
+#define assert_port_profile(port, flgs, caller) do {                    \
     if ((port->flags & (flgs)) != (flgs)) {                             \
       switch (flgs) {                                                   \
       case PIC_PORT_IN:                                                 \
@@ -347,13 +342,8 @@ pic_port_close_port(pic_state *pic)
         pic_errorf(pic, caller ": expected output/binary port");        \
       }                                                                 \
     }                                                                   \
-    if (port->status != stat) {                                         \
-      switch (stat) {                                                   \
-      case PIC_PORT_OPEN:                                               \
-        pic_errorf(pic, caller ": expected open port");                 \
-      case PIC_PORT_CLOSE:                                              \
-        pic_errorf(pic, caller ": expected close port");                \
-      }                                                                 \
+    if ((port->flags & PIC_PORT_OPEN) == 0) {                           \
+      pic_errorf(pic, caller ": expected open port");                   \
     }                                                                   \
   } while (0)
 
@@ -389,7 +379,7 @@ pic_port_get_output_string(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_TEXT, PIC_PORT_OPEN, "get-output-string");
+  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_TEXT, "get-output-string");
 
   return pic_obj_value(pic_get_output_string(pic, port));
 }
@@ -404,8 +394,7 @@ pic_port_open_input_blob(pic_state *pic)
 
   port = (struct pic_port *)pic_obj_alloc(pic, sizeof(struct pic_port *), PIC_TT_PORT);
   port->file = string_open(pic, (const char *)blob->data, blob->len);
-  port->flags = PIC_PORT_IN | PIC_PORT_BINARY;
-  port->status = PIC_PORT_OPEN;
+  port->flags = PIC_PORT_IN | PIC_PORT_BINARY | PIC_PORT_OPEN;
 
   return pic_obj_value(port);
 }
@@ -419,8 +408,7 @@ pic_port_open_output_bytevector(pic_state *pic)
 
   port = (struct pic_port *)pic_obj_alloc(pic, sizeof(struct pic_port *), PIC_TT_PORT);
   port->file = string_open(pic, NULL, 0);
-  port->flags = PIC_PORT_OUT | PIC_PORT_BINARY;
-  port->status = PIC_PORT_OPEN;
+  port->flags = PIC_PORT_OUT | PIC_PORT_BINARY | PIC_PORT_OPEN;
 
   return pic_obj_value(port);
 }
@@ -434,7 +422,7 @@ pic_port_get_output_bytevector(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_BINARY, PIC_PORT_OPEN, "get-output-bytevector");
+  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_BINARY, "get-output-bytevector");
 
   if (port->file->vtable.write != string_write) {
     pic_errorf(pic, "get-output-bytevector: port is not made by open-output-bytevector");
@@ -458,7 +446,7 @@ pic_port_read_char(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, PIC_PORT_OPEN, "read-char");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, "read-char");
 
   if ((c = xfgetc(port->file)) == EOF) {
     return pic_eof_object();
@@ -476,7 +464,7 @@ pic_port_peek_char(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, PIC_PORT_OPEN, "peek-char");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, "peek-char");
 
   if ((c = xfgetc(port->file)) == EOF) {
     return pic_eof_object();
@@ -496,7 +484,7 @@ pic_port_read_line(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, PIC_PORT_OPEN, "read-line");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, "read-line");
 
   buf = pic_open_output_string(pic);
   while ((c = xfgetc(port->file)) != EOF && c != '\n') {
@@ -517,7 +505,7 @@ pic_port_char_ready_p(pic_state *pic)
 {
   struct pic_port *port = pic_stdin(pic);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, PIC_PORT_OPEN, "char-ready?");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, "char-ready?");
 
   pic_get_args(pic, "|p", &port);
 
@@ -533,7 +521,7 @@ pic_port_read_string(pic_state *pic){
 
   pic_get_args(pic, "i|p", &k,  &port);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, PIC_PORT_OPEN, "read-stritg");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_TEXT, "read-stritg");
 
   c = EOF;
   buf = pic_open_output_string(pic);
@@ -560,7 +548,7 @@ pic_port_read_byte(pic_state *pic){
   int c;
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, PIC_PORT_OPEN, "read-u8");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, "read-u8");
   if ((c = xfgetc(port->file)) == EOF) {
     return pic_eof_object();
   }
@@ -576,7 +564,7 @@ pic_port_peek_byte(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, PIC_PORT_OPEN, "peek-u8");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, "peek-u8");
 
   c = xfgetc(port->file);
   if (c == EOF) {
@@ -595,7 +583,7 @@ pic_port_byte_ready_p(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, PIC_PORT_OPEN, "u8-ready?");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, "u8-ready?");
 
   return pic_true_value();      /* FIXME: always returns #t */
 }
@@ -610,7 +598,7 @@ pic_port_read_blob(pic_state *pic)
 
   pic_get_args(pic, "k|p", &k, &port);
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, PIC_PORT_OPEN, "read-bytevector");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, "read-bytevector");
 
   blob = pic_make_blob(pic, k);
 
@@ -644,7 +632,7 @@ pic_port_read_blob_ip(pic_state *pic)
     end = bv->len;
   }
 
-  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, PIC_PORT_OPEN, "read-bytevector!");
+  assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, "read-bytevector!");
 
   if (end < start) {
     pic_errorf(pic, "read-bytevector!: end index must be greater than or equal to start index");
@@ -672,7 +660,7 @@ pic_port_newline(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_TEXT, PIC_PORT_OPEN, "newline");
+  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_TEXT, "newline");
 
   xfputs("\n", port->file);
   return pic_undef_value();
@@ -686,7 +674,7 @@ pic_port_write_char(pic_state *pic)
 
   pic_get_args(pic, "c|p", &c, &port);
 
-  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_TEXT, PIC_PORT_OPEN, "write-char");
+  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_TEXT, "write-char");
 
   xfputc(c, port->file);
   return pic_undef_value();
@@ -709,7 +697,7 @@ pic_port_write_string(pic_state *pic)
     end = INT_MAX;
   }
 
-  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_TEXT, PIC_PORT_OPEN, "write-string");
+  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_TEXT, "write-string");
 
   for (i = start; i < end && str[i] != '\0'; ++i) {
     xfputc(str[i], port->file);
@@ -725,7 +713,7 @@ pic_port_write_byte(pic_state *pic)
 
   pic_get_args(pic, "i|p", &i, &port);
 
-  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_BINARY, PIC_PORT_OPEN, "write-u8");
+  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_BINARY, "write-u8");
 
   xfputc(i, port->file);
   return pic_undef_value();
@@ -749,7 +737,7 @@ pic_port_write_blob(pic_state *pic)
     end = blob->len;
   }
 
-  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_BINARY, PIC_PORT_OPEN, "write-bytevector");
+  assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_BINARY, "write-bytevector");
 
   for (i = start; i < end; ++i) {
     xfputc(blob->data[i], port->file);
@@ -764,7 +752,7 @@ pic_port_flush(pic_state *pic)
 
   pic_get_args(pic, "|p", &port);
 
-  assert_port_profile(port, PIC_PORT_OUT, PIC_PORT_OPEN, "flush-output-port");
+  assert_port_profile(port, PIC_PORT_OUT, "flush-output-port");
 
   xfflush(port->file);
   return pic_undef_value();
@@ -773,9 +761,9 @@ pic_port_flush(pic_state *pic)
 void
 pic_init_port(pic_state *pic)
 {
-  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_define_standard_port(pic, "current-input-port", xstdin, PIC_PORT_IN);
+  pic_define_standard_port(pic, "current-output-port", xstdout, PIC_PORT_OUT);
+  pic_define_standard_port(pic, "current-error-port", xstderr, PIC_PORT_OUT);
 
   pic_defun(pic, "call-with-port", pic_port_call_with_port);
 
diff --git a/extlib/benz/state.c b/extlib/benz/state.c
index 6e11f812..64b58b25 100644
--- a/extlib/benz/state.c
+++ b/extlib/benz/state.c
@@ -254,11 +254,6 @@ pic_open(int argc, char *argv[], char **envp, pic_allocf allocf)
   /* raised error object */
   pic->err = pic_invalid_value();
 
-  /* standard ports */
-  pic->xSTDIN = NULL;
-  pic->xSTDOUT = NULL;
-  pic->xSTDERR = NULL;
-
   /* parameter table */
   pic->ptable = pic_nil_value();
 
@@ -372,11 +367,6 @@ pic_open(int argc, char *argv[], char **envp, pic_allocf allocf)
   /* reader */
   pic->reader = pic_reader_open(pic);
 
-  /* standard I/O */
-  pic->xSTDIN = pic_make_standard_port(pic, xstdin, PIC_PORT_IN);
-  pic->xSTDOUT = pic_make_standard_port(pic, xstdout, PIC_PORT_OUT);
-  pic->xSTDERR = pic_make_standard_port(pic, xstderr, PIC_PORT_OUT);
-
   /* parameter table */
   pic->ptable = pic_cons(pic, pic_obj_value(pic_make_dict(pic)), pic->ptable);
 
diff --git a/extlib/benz/vm.c b/extlib/benz/vm.c
index 791529d0..2f56467f 100644
--- a/extlib/benz/vm.c
+++ b/extlib/benz/vm.c
@@ -467,6 +467,12 @@ pic_funcall(pic_state *pic, struct pic_lib *lib, const char *name, pic_list args
   return pic_apply(pic, pic_proc_ptr(proc), args);
 }
 
+pic_value
+pic_funcall0(pic_state *pic, struct pic_lib *lib, const char *name)
+{
+  return pic_funcall(pic, lib, name, pic_nil_value());
+}
+
 void
 pic_defun(pic_state *pic, const char *name, pic_func_t cfunc)
 {