diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f228ef2..c6bbdb8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -248,8 +248,8 @@ jobs:
     needs: posix
     runs-on: ubuntu-latest
     steps:
-    - name: Coveralls Finished
-      uses: coverallsapp/github-action@master
-      with:
-        github-token: ${{ secrets.github_token }}
-        parallel-finished: true
+      - name: Coveralls Finished
+        uses: coverallsapp/github-action@master
+        with:
+          github-token: ${{ secrets.github_token }}
+          parallel-finished: true
diff --git a/.gitignore b/.gitignore
index e051528..217f5bd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,5 @@
 doc/autodoc.xml
 doc/html
+build
+compile_commands.json
+GNUmakefile
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0ec3256..22e9831 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,42 +1,128 @@
-# Generated by `boostdep --cmake type_index`
+# -----------------------------------------------------------------------------
+# Boost.type_index CMake
+# Handles: no modules, modules, modules + import std;
+# -----------------------------------------------------------------------------
 # Copyright 2020, 2021 Peter Dimov
 # Distributed under the Boost Software License, Version 1.0.
 # https://www.boost.org/LICENSE_1_0.txt
 
-cmake_minimum_required(VERSION 3.5...3.31)
+cmake_minimum_required(VERSION 3.21...4.2)
 
 project(boost_type_index VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
-if (BOOST_USE_MODULES)
+if(PROJECT_IS_TOP_LEVEL)
+    find_package(Boost 1.90.0 CONFIG)
+endif()
+
+# -----------------------------------------------------------------------------
+# User option: enable C++ modules
+# -----------------------------------------------------------------------------
+option(BOOST_USE_MODULES "Build Boost using C++ modules" OFF)
+
+# -----------------------------------------------------------------------------
+# Determine target type and sources
+# -----------------------------------------------------------------------------
+if(BOOST_USE_MODULES)
+
+    # Ensure CMAKE_CXX_STANDARD is set for module detection
+    if(NOT DEFINED CMAKE_CXX_STANDARD)
+        set(CMAKE_CXX_STANDARD 20)
+    endif()
+
     add_library(boost_type_index)
-    target_sources(boost_type_index PUBLIC
-        FILE_SET modules_public TYPE CXX_MODULES FILES modules/boost_type_index.cppm
+
+    target_sources(
+        boost_type_index
+        PUBLIC
+            FILE_SET modules_public
+                TYPE CXX_MODULES
+                FILES modules/boost_type_index.cppm
     )
 
-    target_compile_features(boost_type_index PUBLIC cxx_std_20)
+    # Require C++20 for modules
+    target_compile_features(boost_type_index PUBLIC cxx_std_${CMAKE_CXX_STANDARD})
+    # Define macro indicating modules usage
     target_compile_definitions(boost_type_index PUBLIC BOOST_USE_MODULES)
-    if (CMAKE_CXX_COMPILER_IMPORT_STD)
-        target_compile_definitions(boost_type_index PRIVATE BOOST_TYPE_INDEX_USE_STD_MODULE)
-        message(STATUS "Using `import std;`")
+
+    # Check if import std; is available for the current standard
+    if(${CMAKE_CXX_STANDARD} IN_LIST CMAKE_CXX_COMPILER_IMPORT_STD)
+        target_compile_definitions(boost_type_index PUBLIC BOOST_TYPE_INDEX_USE_STD_MODULE)
+        set_property(TARGET boost_type_index CXX_MODULE_STD ON)
+        message(STATUS "Boost.type_index: Using `import std;`")
     else()
-        message(STATUS "`import std;` is not awailable")
+        message(WARNING "Boost.type_index: `import std;` is not available for C++${CMAKE_CXX_STANDARD}")
     endif()
+
     set(__scope PUBLIC)
+
 else()
+
+    # Modules disabled -> INTERFACE library
     add_library(boost_type_index INTERFACE)
+
+    # If modules are disabled, require C++17 for headers
+    target_compile_features(boost_type_index INTERFACE cxx_std_17)
+
+    # Verify interface headers only at top level
+    if(PROJECT_IS_TOP_LEVEL)
+        set(CMAKE_VERIFY_INTERFACE_HEADER_SETS ON)
+    endif()
+
     set(__scope INTERFACE)
+
 endif()
 
-target_include_directories(boost_type_index ${__scope} include)
-add_library(Boost::type_index ALIAS boost_type_index)
+# -----------------------------------------------------------------------------
+# Include headers
+# -----------------------------------------------------------------------------
+if(BOOST_USE_MODULES)
+    target_sources(
+        boost_type_index
+        PUBLIC
+            FILE_SET headers_public
+                TYPE HEADERS
+                BASE_DIRS include
+                FILES
+                    include/boost/type_index.hpp
+                    include/boost/type_index/runtime_cast.hpp
+                    include/boost/type_index/stl_type_index.hpp
+                    include/boost/type_index/detail/compile_time_type_info.hpp
+                    include/boost/type_index/detail/stl_register_class.hpp
+                    include/boost/type_index/detail/config.hpp
+                    include/boost/type_index/detail/ctti_register_class.hpp
+                    include/boost/type_index/ctti_type_index.hpp
+                    include/boost/type_index/runtime_cast/std_shared_ptr_cast.hpp
+                    include/boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp
+                    include/boost/type_index/runtime_cast/register_runtime_class.hpp
+                    include/boost/type_index/runtime_cast/pointer_cast.hpp
+                    include/boost/type_index/runtime_cast/reference_cast.hpp
+                    include/boost/type_index/runtime_cast/boost_shared_ptr_cast.hpp
+                    include/boost/type_index/type_index_facade.hpp
+    )
+else()
+    target_include_directories(boost_type_index ${__scope} include)
+endif()
+
+# -----------------------------------------------------------------------------
+# Link dependencies
+# -----------------------------------------------------------------------------
+if(PROJECT_IS_TOP_LEVEL)
+    target_link_libraries(boost_any ${__scope} Boost::headers)
+else()
+    target_link_libraries(boost_type_index
+        ${__scope}
+        Boost::config
+        Boost::container_hash
+        Boost::throw_exception
+    )
+endif()
 
-target_link_libraries(boost_type_index
-  ${__scope}
-    Boost::config
-    Boost::container_hash
-    Boost::throw_exception
-)
+# Alias for convenient import
+add_library(Boost::type_index ALIAS boost_type_index)
 
+# -----------------------------------------------------------------------------
+# Testing
+# -----------------------------------------------------------------------------
 if(BUILD_TESTING)
-  add_subdirectory(test)
+    add_subdirectory(test)
 endif()
diff --git a/modules/boost_type_index.cppm b/modules/boost_type_index.cppm
index 6f53dda..7023476 100644
--- a/modules/boost_type_index.cppm
+++ b/modules/boost_type_index.cppm
@@ -9,8 +9,6 @@
 module;
 
 #include <version>
-#include <cstddef>
-#include <cstdint>
 
 #if __has_include(<cxxabi.h>)
 #  include <cxxabi.h>
@@ -21,7 +19,11 @@ module;
 #include <boost/container_hash/hash.hpp>
 #include <boost/throw_exception.hpp>
 
-#ifndef BOOST_TYPE_INDEX_USE_STD_MODULE
+#ifdef BOOST_TYPE_INDEX_USE_STD_MODULE
+import std;
+#else
+#include <cstdint>
+#include <cstddef>
 #include <cstring>
 #include <cstdlib>
 #include <iosfwd>
@@ -36,12 +38,6 @@ module;
 
 export module boost.type_index;
 
-#ifdef BOOST_TYPE_INDEX_USE_STD_MODULE
-// Should not be in the global module fragment
-// https://eel.is/c++draft/module#global.frag-1
-import std;
-#endif
-
 #ifdef __clang__
 #   pragma clang diagnostic ignored "-Winclude-angled-in-module-purview"
 #endif
diff --git a/test/cmake_subdir_test/CMakeLists.txt b/test/cmake_subdir_test/CMakeLists.txt
index 698e472..4bae3c2 100644
--- a/test/cmake_subdir_test/CMakeLists.txt
+++ b/test/cmake_subdir_test/CMakeLists.txt
@@ -2,7 +2,7 @@
 # Distributed under the Boost Software License, Version 1.0.
 # See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt
 
-cmake_minimum_required(VERSION 3.5...4.0)
+cmake_minimum_required(VERSION 3.21...4.2)
 
 project(type_index_subdir_test LANGUAGES CXX)
 
@@ -16,14 +16,16 @@ foreach(dep IN ITEMS
   smart_ptr
   throw_exception
   unordered
-  predef)
+  predef
+)
     add_subdirectory(../../../${dep} boostorg/${dep})
 endforeach()
+
 add_subdirectory(../../ boostorg/type_index)
 
 enable_testing()
 
-if (BOOST_USE_MODULES)
+if(BOOST_USE_MODULES)
     add_executable(boost_type_index_module_usage ../../modules/usage_sample.cpp)
     target_link_libraries(boost_type_index_module_usage PRIVATE Boost::type_index)
     add_test(NAME boost_type_index_module_usage COMMAND boost_type_index_module_usage)
@@ -32,18 +34,18 @@ if (BOOST_USE_MODULES)
     add_executable(boost_type_index_module_usage_mu ../../modules/usage_test_mu1.cpp ../../modules/usage_test_mu2.cpp)
     target_link_libraries(boost_type_index_module_usage_mu PRIVATE Boost::type_index)
     add_test(NAME boost_type_index_module_usage_mu COMMAND boost_type_index_module_usage_mu)
+else()
+    list(APPEND RUN_TESTS_SOURCES
+        compare_ctti_stl.cpp
+        ctti_print_name.cpp
+        track_13621.cpp
+        type_index_runtime_cast_test.cpp
+        type_index_test.cpp
+    )
 endif()
 
-list(APPEND RUN_TESTS_SOURCES
-    compare_ctti_stl.cpp
-    ctti_print_name.cpp
-    track_13621.cpp
-    type_index_runtime_cast_test.cpp
-    type_index_test.cpp
-)
-
-foreach (testsourcefile ${RUN_TESTS_SOURCES})
-    get_filename_component(testname ${testsourcefile} NAME_WLE)
+foreach(testsourcefile ${RUN_TESTS_SOURCES})
+    get_filename_component(testname ../${testsourcefile} NAME_WLE)
     add_executable(${PROJECT_NAME}_${testname} ../${testsourcefile})
     target_link_libraries(${PROJECT_NAME}_${testname} Boost::type_index Boost::smart_ptr)
     add_test(NAME ${PROJECT_NAME}_${testname} COMMAND ${PROJECT_NAME}_${testname})