diff --git a/pixivclient.cpp b/pixivclient.cpp
index f14172d..85a6700 100644
--- a/pixivclient.cpp
+++ b/pixivclient.cpp
@@ -9,7 +9,6 @@ using namespace std::string_literals;
 
 static const constexpr char* touch_user_agent = "Mozilla/5.0 (Android 12; Mobile; rv:97.0) Gecko/97.0 Firefox/97.0";
 static const constexpr char* desktop_user_agent = "Mozilla/5.0 (Windows NT 10.0; rv:111.0) Gecko/20100101 Firefox/111.0";
-static void to_lower(std::string& str);
 
 PixivClient::PixivClient(Redis* redis) : _redis(redis) {
     this->_www_pixiv_net_client.set_keep_alive(true);
@@ -46,7 +45,6 @@ Illust PixivClient::get_illust(uint64_t illust_id) {
 }
 
 SearchResults PixivClient::search_illusts(std::string query, size_t page, const std::string& order) {
-    to_lower(query);
     httplib::Params params = {
         {"lang", "en"},
         {"mode", "all"},
@@ -64,7 +62,6 @@ SearchResults PixivClient::search_illusts(std::string query, size_t page, const
 }
 
 std::vector<SearchSuggestion> PixivClient::get_search_suggestions(std::string query) {
-    to_lower(query);
     std::string body = [&]() {
         std::string cache_key = "pixwhile:searchsugg:"s + std::to_string(FastHash(query.data(), query.size(), 0));
         if (this->_redis) {
@@ -142,12 +139,3 @@ bool PixivClient::i_pximg_url_valid(const std::string& path) {
     }
     return res->status >= 200 && res->status <= 200;
 }
-
-
-static void to_lower(std::string& str) {
-    for (size_t i = 0; i < str.size(); i++) {
-        if (str[i] >= 'A' && str[i] <= 'Z') {
-            str[i] = static_cast<char>(str[i] - 'A' + 'a');
-        }
-    }
-}