diff --git a/include/picrin.h b/include/picrin.h
index 27c1e210..1da8a491 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -164,8 +164,9 @@ bool pic_interned_p(pic_state *, pic_sym);
 
 char *pic_strdup(pic_state *, const char *);
 char *pic_strndup(pic_state *, const char *, size_t);
-struct pic_string *pic_str_new(pic_state *, const char *, size_t); /* the 2nd arg may be NULL for empty string */
-struct pic_string *pic_str_new_cstr(pic_state *, const char *);
+pic_str *pic_str_new(pic_state *, const char * /* nullable */, size_t);
+pic_str *pic_str_new_cstr(pic_state *, const char *);
+
 pic_value pic_format(pic_state *, const char *, ...);
 pic_value pic_vformat(pic_state *, const char *, va_list);
 pic_value pic_vfformat(pic_state *, XFILE *, const char *, va_list);
diff --git a/src/string.c b/src/string.c
index 67b98692..f7437c37 100644
--- a/src/string.c
+++ b/src/string.c
@@ -8,10 +8,10 @@
 #include "picrin/pair.h"
 #include "picrin/port.h"
 
-struct pic_string *
+pic_str *
 pic_str_new(pic_state *pic, const char *cstr, size_t len)
 {
-  struct pic_string *str;
+  pic_str *str;
   char *copy;
 
   if (cstr) {
@@ -20,12 +20,18 @@ pic_str_new(pic_state *pic, const char *cstr, size_t len)
     copy = (char *)pic_alloc(pic, len);
   }
 
-  str = (struct pic_string *)pic_obj_alloc(pic, sizeof(struct pic_string), PIC_TT_STRING);
+  str = (pic_str *)pic_obj_alloc(pic, sizeof(pic_str), PIC_TT_STRING);
   str->len = len;
   str->str = copy;
   return str;
 }
 
+pic_str *
+pic_str_new_cstr(pic_state *pic, const char *cstr)
+{
+  return pic_str_new(pic, cstr, strlen(cstr));
+}
+
 pic_value
 pic_vfformat(pic_state *pic, XFILE *file, const char *fmt, va_list ap)
 {
@@ -119,15 +125,6 @@ pic_format(pic_state *pic, const char *fmt, ...)
   return objs;
 }
 
-struct pic_string *
-pic_str_new_cstr(pic_state *pic, const char *cstr)
-{
-  size_t len;
-
-  len = strlen(cstr);
-  return pic_str_new(pic, cstr, len);
-}
-
 static pic_value
 pic_str_string_p(pic_state *pic)
 {
@@ -230,7 +227,7 @@ pic_str_string_copy(pic_state *pic)
   size_t len, start, end, i;
   char *str;
   int n;
-  struct pic_string *copy;
+  pic_str *copy;
 
   n = pic_get_args(pic, "s|ii", &str, &len, &start, &end);