diff --git a/builtin-functions/kphp-light/stdlib/vkext-functions.txt b/builtin-functions/kphp-light/stdlib/vkext-functions.txt
index b18580fd41..18a68e6f0c 100644
--- a/builtin-functions/kphp-light/stdlib/vkext-functions.txt
+++ b/builtin-functions/kphp-light/stdlib/vkext-functions.txt
@@ -1,7 +1,5 @@
 <?php
 
-// ===== SUPPORTED =====
-
 function vk_utf8_to_win ($text ::: string, $max_len ::: int = 0, $exit_on_error ::: bool = false) ::: string;
 
 function vk_win_to_utf8 ($text ::: string, $escape ::: bool = true) ::: string;
@@ -36,7 +34,4 @@ function vk_stats_hll_unpack($hll ::: string) ::: string | false;
 
 function vk_stats_hll_is_packed($hll ::: string) ::: bool;
 
-// ===== UNSUPPORTED =====
-
-/** @kphp-extern-func-info stub generation-required */
 function vk_flex ($name ::: string, $case_name ::: string, $sex ::: int, $type ::: string, $lang_id ::: int = 0) ::: string;
diff --git a/compiler/compiler-settings.cpp b/compiler/compiler-settings.cpp
index ad289f9171..bbe36c915f 100644
--- a/compiler/compiler-settings.cpp
+++ b/compiler/compiler-settings.cpp
@@ -389,11 +389,16 @@ void CompilerSettings::init() {
 
 #if defined(__APPLE__)
   append_if_doesnt_contain(ld_flags.value_, system_installed_static_libs, "-l");
-  auto flex_prefix = kphp_src_path.value_ + "objs/flex/lib";
-  append_if_doesnt_contain(ld_flags.value_, vk::to_array({"vk-flex-data"}), flex_prefix, ".a");
+  if (!is_k2_mode) {
+    auto flex_prefix = kphp_src_path.value_ + "objs/flex/lib";
+    append_if_doesnt_contain(ld_flags.value_, vk::to_array({"vk-flex-data"}), flex_prefix, ".a");
+  }
   system_installed_dynamic_libs.emplace_back("iconv");
 #else
-  system_installed_static_libs.emplace_back("vk-flex-data");
+  if (!is_k2_mode) {
+    // In the case of K2, the vk-flex-data library is compiled into runtime-light
+    system_installed_static_libs.emplace_back("vk-flex-data");
+  }
   append_if_doesnt_contain(ld_flags.value_, system_installed_static_libs, "-l:lib", ".a");
   system_installed_dynamic_libs.emplace_back("rt");
 #endif
diff --git a/flex/flex.cmake b/flex/flex.cmake
index c3061f7c4a..8a05d2b42a 100644
--- a/flex/flex.cmake
+++ b/flex/flex.cmake
@@ -24,6 +24,11 @@ add_dependencies(flex-data-src-pic flex-data)
 vk_add_library_no_pic(flex-data-src-no-pic OBJECT ${FLEX_SOURCES})
 add_dependencies(flex-data-src-no-pic flex-data)
 
+if (COMPILE_RUNTIME_LIGHT)
+    target_compile_options(flex-data-src-pic PUBLIC -stdlib=libc++ ${RUNTIME_LIGHT_VISIBILITY})
+    target_link_options(flex-data-src-pic PUBLIC -stdlib=libc++)
+endif()
+
 vk_add_library_pic(flex_data_shared-pic SHARED $<TARGET_OBJECTS:flex-data-src-pic>)
 add_dependencies(flex_data_shared-pic flex-data-src-pic)
 
diff --git a/runtime-common/stdlib/vkext/vkext-functions.cpp b/runtime-common/stdlib/vkext/vkext-functions.cpp
index f339532df3..24058f467d 100644
--- a/runtime-common/stdlib/vkext/vkext-functions.cpp
+++ b/runtime-common/stdlib/vkext/vkext-functions.cpp
@@ -6,6 +6,11 @@
 #include <array>
 #include <cstdio>
 
+#include "flex/flex.h"
+
+#include "runtime-common/core/utils/kphp-assert-core.h"
+#include "runtime-common/stdlib/string/string-context.h"
+
 namespace {
 
 constexpr std::array<int, 256> utf8_to_win_convert_0x400 = {
@@ -458,3 +463,19 @@ string f$vk_whitespace_pack(const string& str, bool html_opt) noexcept {
   }
   return buffered.result;
 }
+
+string f$vk_flex(const string& name, const string& case_name, int64_t sex, const string& type, int64_t lang_id) noexcept {
+  constexpr size_t ERROR_MSG_BUG_SIZE{1000};
+  std::array<char, ERROR_MSG_BUG_SIZE> error_msg_buffer{'\0'};
+
+  auto* static_buffer{StringLibContext::get().static_buf.get()};
+  std::string_view res = flex(std::string_view{name.c_str(), name.size()}, std::string_view{case_name.c_str(), case_name.size()}, sex == 1,
+                              std::string_view{type.c_str(), type.size()}, lang_id, static_buffer, error_msg_buffer.data(), ERROR_MSG_BUG_SIZE);
+  if (error_msg_buffer[0] != '\0') {
+    php_warning("%s", error_msg_buffer.data());
+  }
+  if (res.data() == name.c_str()) {
+    return name;
+  }
+  return string{res.data(), static_cast<string::size_type>(res.size())};
+}
diff --git a/runtime-common/stdlib/vkext/vkext-functions.h b/runtime-common/stdlib/vkext/vkext-functions.h
index 81265ced6e..2c39c87d3a 100644
--- a/runtime-common/stdlib/vkext/vkext-functions.h
+++ b/runtime-common/stdlib/vkext/vkext-functions.h
@@ -50,3 +50,5 @@ inline string f$vk_sp_to_cyrillic(const string& s) noexcept {
 inline string f$vk_sp_words_only(const string& s) noexcept {
   return vkext_impl_::sp_words_only(s);
 }
+
+string f$vk_flex(const string& name, const string& case_name, int64_t sex, const string& type, int64_t lang_id = 0) noexcept;
diff --git a/runtime-light/runtime-light.cmake b/runtime-light/runtime-light.cmake
index 3cc64e6e03..0ea0cfa0dc 100644
--- a/runtime-light/runtime-light.cmake
+++ b/runtime-light/runtime-light.cmake
@@ -64,7 +64,7 @@ set(RUNTIME_LIGHT_LINK_LIBS "${KPHP_TIMELIB_PIC_LIBRARIES} ${PCRE2_PIC_LIBRARIES
 vk_add_library_pic(kphp-light-runtime-pic STATIC)
 target_compile_options(kphp-light-runtime-pic PUBLIC ${RUNTIME_LIGHT_COMPILE_FLAGS})
 target_link_options(kphp-light-runtime-pic PUBLIC ${RUNTIME_LIGHT_LINK_FLAGS})
-target_link_libraries(kphp-light-runtime-pic PUBLIC vk::pic::light-common vk::pic::unicode vk::pic::runtime-light vk::pic::runtime-common)
+target_link_libraries(kphp-light-runtime-pic PUBLIC vk::pic::flex-data-src vk::pic::light-common vk::pic::unicode vk::pic::runtime-light vk::pic::runtime-common)
 
 set_target_properties(kphp-light-runtime-pic PROPERTIES LIBRARY_OUTPUT_NAME libkphp-light-runtime.a)
 
diff --git a/runtime/misc.cpp b/runtime/misc.cpp
index 11bae7501d..82f7c64510 100644
--- a/runtime/misc.cpp
+++ b/runtime/misc.cpp
@@ -12,6 +12,7 @@
 #include <unistd.h>
 
 #include "runtime-common/stdlib/serialization/json-functions.h"
+#include "runtime-common/stdlib/vkext/vkext-functions.h"
 #include "runtime/context/runtime-context.h"
 #include "runtime/critical_section.h"
 #include "runtime/datetime/datetime_functions.h"
@@ -20,7 +21,6 @@
 #include "runtime/interface.h"
 #include "runtime/math_functions.h"
 #include "runtime/string_functions.h"
-#include "runtime/vkext.h"
 #include "server/json-logger.h"
 #include "server/php-engine-vars.h"
 
diff --git a/runtime/runtime.cmake b/runtime/runtime.cmake
index 9c161d5864..1525041cc9 100644
--- a/runtime/runtime.cmake
+++ b/runtime/runtime.cmake
@@ -116,7 +116,6 @@ prepend(KPHP_RUNTIME_SOURCES ${BASE_DIR}/runtime/
         uber-h3.cpp
         udp.cpp
         tcp.cpp
-        vkext.cpp
         ffi.cpp
         zlib.cpp
         zstd.cpp)
diff --git a/runtime/vkext.cpp b/runtime/vkext.cpp
deleted file mode 100644
index 9771e1edd1..0000000000
--- a/runtime/vkext.cpp
+++ /dev/null
@@ -1,27 +0,0 @@
-// Compiler for PHP (aka KPHP)
-// Copyright (c) 2020 LLC «V Kontakte»
-// Distributed under the GPL v3 License, see LICENSE.notice.txt
-
-#include "runtime/vkext.h"
-
-#include "common/wrappers/string_view.h"
-#include "flex/flex.h"
-#include "runtime/php_assert.h"
-
-#define BUFF_LEN (1 << 16)
-static char buff[BUFF_LEN];
-
-string f$vk_flex(const string& name, const string& case_name, int64_t sex, const string& type, int64_t lang_id) noexcept {
-  constexpr size_t ERROR_MSG_BUG_SIZE = 1000;
-  static char ERROR_MSG_BUF[ERROR_MSG_BUG_SIZE] = {'\0'};
-  ERROR_MSG_BUF[0] = '\0';
-  vk::string_view res = flex(vk::string_view{name.c_str(), name.size()}, vk::string_view{case_name.c_str(), case_name.size()}, sex == 1,
-                             vk::string_view{type.c_str(), type.size()}, lang_id, buff, ERROR_MSG_BUF, ERROR_MSG_BUG_SIZE);
-  if (ERROR_MSG_BUF[0] != '\0') {
-    php_warning("%s", ERROR_MSG_BUF);
-  }
-  if (res.data() == name.c_str()) {
-    return name;
-  }
-  return string{res.data(), static_cast<string::size_type>(res.size())};
-}
diff --git a/runtime/vkext.h b/runtime/vkext.h
deleted file mode 100644
index f33a9ae344..0000000000
--- a/runtime/vkext.h
+++ /dev/null
@@ -1,11 +0,0 @@
-// Compiler for PHP (aka KPHP)
-// Copyright (c) 2020 LLC «V Kontakte»
-// Distributed under the GPL v3 License, see LICENSE.notice.txt
-
-#pragma once
-
-#include "runtime-common/core/runtime-core.h"
-
-#include "runtime-common/stdlib/vkext/vkext-functions.h"
-
-string f$vk_flex(const string& name, const string& case_name, int64_t sex, const string& type, int64_t lang_id = 0) noexcept;
diff --git a/tests/cpp/runtime/flex-test.cpp b/tests/cpp/runtime/flex-test.cpp
index f3e88cb55a..46122b490d 100644
--- a/tests/cpp/runtime/flex-test.cpp
+++ b/tests/cpp/runtime/flex-test.cpp
@@ -3,7 +3,7 @@
 #include <string>
 #include <vector>
 
-#include "runtime/vkext.h"
+#include "runtime-common/stdlib/vkext/vkext-functions.h"
 
 using casing_table = std::array<std::string, 6>;
 
diff --git a/tests/phpt/dl/474_flex.php b/tests/phpt/dl/474_flex.php
index ce61cef0e9..e1e26791df 100644
--- a/tests/phpt/dl/474_flex.php
+++ b/tests/phpt/dl/474_flex.php
@@ -1,4 +1,4 @@
-@ok k2_skip benchmark
+@ok benchmark
 <?php
 
 $langs = array (0, 1, 2, 8, 11, 19, 21, 51, 52, 91, 100, 777, 888, 999);