diff --git a/runtime-light/stdlib/string/string-functions.h b/runtime-light/stdlib/string/string-functions.h
index aa6b147dde..38e13702d7 100644
--- a/runtime-light/stdlib/string/string-functions.h
+++ b/runtime-light/stdlib/string/string-functions.h
@@ -17,12 +17,12 @@ inline string f$prepare_search_query(const string& query) noexcept {
 
 inline Optional<string> f$setlocale(int64_t category, const string& locale) noexcept {
   const int32_t i32category{static_cast<int32_t>(category)};
-  if (k2::uselocale(i32category, {locale.c_str(), locale.size()}) != k2::errno_ok) {
+  if (const std::string_view sv_locale{locale.c_str(), locale.size()}; sv_locale != "0" && k2::uselocale(i32category, sv_locale) != k2::errno_ok) {
     return false;
   }
   const auto opt_locale_name{k2::current_locale_name(i32category)};
   if (!opt_locale_name.has_value()) [[unlikely]] {
     return false;
   }
-  return opt_locale_name->data();
+  return string{opt_locale_name->data(), static_cast<string::size_type>(opt_locale_name->size())};
 }
diff --git a/tests/phpt/dl/1048_setlocale.php b/tests/phpt/dl/1048_setlocale.php
new file mode 100644
index 0000000000..8d55e989f4
--- /dev/null
+++ b/tests/phpt/dl/1048_setlocale.php
@@ -0,0 +1,94 @@
+@ok
+<?php
+
+function setlocale_zero() {
+    var_dump("setlocale_zero");
+
+    var_dump("LC_CTYPE 0 -> " . setlocale(LC_CTYPE, "0"));
+    var_dump("LC_NUMERIC 0 -> " . setlocale(LC_NUMERIC, "0"));
+    var_dump("LC_TIME 0 -> " . setlocale(LC_TIME, "0"));
+    var_dump("LC_COLLATE 0 -> " . setlocale(LC_COLLATE, "0"));
+    var_dump("LC_MONETARY 0 -> " . setlocale(LC_MONETARY, "0"));
+    var_dump("LC_ALL 0 -> " . setlocale(LC_ALL, "0"));
+}
+
+function setlocale_return_empty() {
+    var_dump("setlocale_empty");
+
+    var_dump("LC_CTYPE \"\" -> " . setlocale(LC_CTYPE, ""));
+    var_dump("LC_NUMERIC \"\" -> " . setlocale(LC_NUMERIC, ""));
+    var_dump("LC_TIME \"\" -> " . setlocale(LC_TIME, ""));
+    var_dump("LC_COLLATE \"\" -> " . setlocale(LC_COLLATE, ""));
+    var_dump("LC_MONETARY \"\" -> " . setlocale(LC_MONETARY, ""));
+    var_dump("LC_ALL \"\" -> " . setlocale(LC_ALL, ""));
+
+    var_dump("check other (1)");
+    setlocale_zero();
+}
+
+function setlocale_return_set_ru_RU_CP1251() {
+    var_dump("setlocale_set_ru_RU_CP1251");
+
+    var_dump("LC_ALL \"\" -> " . setlocale(LC_ALL, "")); // unset all
+
+    var_dump("LC_CTYPE ru_RU.CP1251 -> " . setlocale(LC_CTYPE, "ru_RU.CP1251"));
+    var_dump("LC_CTYPE 0 -> " . setlocale(LC_CTYPE, "0"));
+
+    var_dump("LC_NUMERIC ru_RU.CP1251 -> " . setlocale(LC_NUMERIC, "ru_RU.CP1251"));
+    var_dump("LC_NUMERIC 0 -> " . setlocale(LC_NUMERIC, "0"));
+
+    var_dump("LC_TIME ru_RU.CP1251 -> " . setlocale(LC_TIME, "ru_RU.CP1251"));
+    var_dump("LC_TIME 0 -> " . setlocale(LC_TIME, "0"));
+
+    var_dump("LC_COLLATE ru_RU.CP1251 -> " . setlocale(LC_COLLATE, "ru_RU.CP1251"));
+    var_dump("LC_COLLATE 0 -> " . setlocale(LC_COLLATE, "0"));
+
+    var_dump("LC_MONETARY ru_RU.CP1251 -> " . setlocale(LC_MONETARY, "ru_RU.CP1251"));
+    var_dump("LC_MONETARY 0 -> " . setlocale(LC_MONETARY, "0"));
+
+    var_dump("LC_ALL 0 -> " . setlocale(LC_ALL, "0"));
+
+    var_dump("LC_ALL \"\" -> " . setlocale(LC_ALL, "")); // unset all
+
+    var_dump("check other (2)");
+    setlocale_zero();
+
+    var_dump("LC_ALL ru_RU.CP1251 -> " . setlocale(LC_ALL, "ru_RU.CP1251"));
+
+    var_dump("check other (3)");
+    setlocale_zero();
+
+    var_dump("LC_ALL \"\" -> " . setlocale(LC_ALL, "")); // unset all
+}
+
+function setlocale_return_correct_LC_ALL_changes() {
+    var_dump("setlocale_correct_LC_ALL_changes");
+
+    var_dump("LC_ALL en_US.UTF-8 -> " . setlocale(LC_ALL, "en_US.UTF-8"));
+    var_dump("LC_ALL 0 -> " . setlocale(LC_ALL, "0"));
+
+    var_dump("LC_COLLATE ru_RU.CP1251 -> " . setlocale(LC_COLLATE, "ru_RU.CP1251"));
+    var_dump("LC_ALL 0 -> " . setlocale(LC_ALL, "0"));
+
+    var_dump("LC_COLLATE en_US.UTF-8 -> " . setlocale(LC_COLLATE, "en_US.UTF-8"));
+    var_dump("LC_ALL 0 -> " . setlocale(LC_ALL, "0"));
+}
+
+
+function setlocale_numeric_cp1251() {
+    function printf_numeric() {
+        printf("%.2f\n", 1234.56);
+    }
+
+    var_dump("setlocale_numeric_cp1251");
+    setlocale(LC_NUMERIC, 'ru_RU.CP1251');
+    printf_numeric();
+    setlocale(LC_NUMERIC, 'C');
+    printf_numeric();
+}
+
+
+setlocale_return_empty();
+setlocale_return_set_ru_RU_CP1251();
+setlocale_return_correct_LC_ALL_changes();
+setlocale_numeric_cp1251();