diff --git a/include/picrin/string.h b/include/picrin/string.h
index 5dc81bf1..da342bd5 100644
--- a/include/picrin/string.h
+++ b/include/picrin/string.h
@@ -22,13 +22,13 @@ pic_str *pic_str_new(pic_state *, const char * /* nullable */, size_t);
 pic_str *pic_str_new_cstr(pic_state *, const char *);
 pic_str *pic_str_new_fill(pic_state *, size_t, char);
 
-size_t pic_strlen(pic_state *, pic_str *);
+size_t pic_strlen(pic_str *);
 char pic_str_ref(pic_state *, pic_str *, size_t);
 void pic_str_set(pic_state *, pic_str *, size_t, char);
 
 pic_str *pic_strcat(pic_state *, pic_str *, pic_str *);
 pic_str *pic_substr(pic_state *, pic_str *, size_t, size_t);
-int pic_strcmp(pic_state *, pic_str *, pic_str *);
+int pic_strcmp(pic_str *, pic_str *);
 
 pic_value pic_format(pic_state *, const char *, ...);
 pic_value pic_vformat(pic_state *, const char *, va_list);
diff --git a/src/string.c b/src/string.c
index b6345ed0..2bcdce92 100644
--- a/src/string.c
+++ b/src/string.c
@@ -49,10 +49,8 @@ pic_str_new_fill(pic_state *pic, size_t len, char fill)
 }
 
 size_t
-pic_strlen(pic_state *pic, pic_str *str)
+pic_strlen(pic_str *str)
 {
-  UNUSED(pic);
-
   return str->len;
 }
 
@@ -104,10 +102,8 @@ pic_substr(pic_state *pic, pic_str *str, size_t s, size_t e)
 }
 
 int
-pic_strcmp(pic_state *pic, pic_str *str1, pic_str *str2)
+pic_strcmp(pic_str *str1, pic_str *str2)
 {
-  UNUSED(pic);
-
   return strcmp(str1->str, str2->str);
 }
 
@@ -232,7 +228,7 @@ pic_str_string_length(pic_state *pic)
 
   pic_get_args(pic, "s", &str);
 
-  return pic_int_value(pic_strlen(pic, str));
+  return pic_int_value(pic_strlen(str));
 }
 
 static pic_value
@@ -277,7 +273,7 @@ pic_str_string_set(pic_state *pic)
       if (! pic_str_p(argv[i])) {                                       \
 	return pic_false_value();                                       \
       }                                                                 \
-      if (! (pic_strcmp(pic, pic_str_ptr(argv[i-1]), pic_str_ptr(argv[i])) op 0)) { \
+      if (! (pic_strcmp(pic_str_ptr(argv[i-1]), pic_str_ptr(argv[i])) op 0)) { \
 	return pic_false_value();                                       \
       }                                                                 \
     }                                                                   \
@@ -302,7 +298,7 @@ pic_str_string_copy(pic_state *pic)
   case 1:
     start = 0;
   case 2:
-    end = pic_strlen(pic, str);
+    end = pic_strlen(str);
   }
 
   return pic_obj_value(pic_substr(pic, str, start, end));
@@ -320,7 +316,7 @@ pic_str_string_copy_ip(pic_state *pic)
   case 3:
     start = 0;
   case 4:
-    end = pic_strlen(pic, from);
+    end = pic_strlen(from);
   }
 
   while (start < end) {
@@ -361,7 +357,7 @@ pic_str_string_fill_ip(pic_state *pic)
   case 1:
     start = 0;
   case 2:
-    end = pic_strlen(pic, str);
+    end = pic_strlen(str);
   }
 
   while (start < end) {