diff --git a/.github/workflows/cmake-multi-platform.yml b/.github/workflows/cmake-multi-platform.yml
index 2bbe9ec..2fffdc1 100644
--- a/.github/workflows/cmake-multi-platform.yml
+++ b/.github/workflows/cmake-multi-platform.yml
@@ -35,8 +35,8 @@ jobs:
             c_compiler: gcc
             cpp_compiler: g++
           - os: ubuntu-24.04
-            c_compiler: clang
-            cpp_compiler: clang++
+            c_compiler: clang-19
+            cpp_compiler: clang++-19
           - os: macos-15
             c_compiler: clang
             cpp_compiler: clang++
@@ -73,7 +73,15 @@ jobs:
 
     - name: Install dependencies (Linux)
       if: runner.os == 'Linux'
-      run: sudo apt-get install -y libfmt-dev clang-tidy clang-format cmake-format cppcheck iwyu libc++-dev libc++abi-dev
+      run: |
+        sudo apt-get install -y clang-tidy-19 clang-format-19 libclang-19-dev \
+                                libc++-dev libc++abi-dev libfmt-dev cmake-format cppcheck 
+        cd ..
+        git clone https://github.com/include-what-you-use/include-what-you-use.git
+        cd include-what-you-use
+        mkdir build && cd build
+        cmake -DCMAKE_PREFIX_PATH=/usr/lib/llvm-19 ..
+        make -j install
 
     - name: Install dependencies (Windows)
       if: runner.os == 'Windows' && matrix.format_lib == 'fmtlib'
diff --git a/.iwyu-mappings b/.iwyu-mappings
index 074f5b4..62ebdf4 100644
--- a/.iwyu-mappings
+++ b/.iwyu-mappings
@@ -8,17 +8,22 @@
     { include: [ "@<__mutex/.*>", "private", "<mutex>", "public" ] },
     { include: [ "@<__exception/.*>", "private", "<exception>", "public" ] },
     { include: [ "@<__system_error/.*>", "private", "<system_error>", "public" ] },
+    { include: [ "@<__ostream/.*>", "private", "<ostream>", "public" ] },
     { include: [ "<__fwd/string_view.h>", "private", "<string_view>", "public" ] },
     { include: [ "<__hash_table>", "private", "<unordered_map>", "public" ] },
     { include: [ "<__hash_table>", "private", "<unordered_set>", "public" ] },
     { include: [ "<__locale>", "private", "<locale>", "public" ] },
     # Bug on stdlibc++: std::tm is not from <cwchar>
-    { symbol: [ "std::tm", "private", "<ctime>", "public" ] },
-    # Bug on stdlibc++ w/o fmtlib: std::pair is not from <iterator>
+    #{ symbol: [ "std::tm", "private", "<ctime>", "public" ] },
+    # Bug on stdlibc++: std::nullptr_t is not from <version>
+    { symbol: [ "std::nullptr_t", "private", "<cstddef>", "public" ] },
+    # Bug on stdlibc++: std::pair is not from <iterator>
     { symbol: [ "std::pair", "private", "<utility>", "public" ] },
+    # Bug on stdlibc++ with fmtlib: std::vector is not from <format>
+    { symbol: [ "std::vector", "private", "<vector>", "public" ] },
     # Bug on libc++ w/o fmtlib: std::reference_wrapper is not from <type_traits>
-    { symbol: [ "std::reference_wrapper", "private", "<functional>", "public" ] },
-    { symbol: [ "std::copy", "private", "<algorithm>", "public" ] },
+    #{ symbol: [ "std::reference_wrapper", "private", "<functional>", "public" ] },
+    #{ symbol: [ "std::copy", "private", "<algorithm>", "public" ] },
     # Bug on fmtlib: format_error::~format_error is not from "format.h"
-    { include: [ "\"format.h\"", "private", "\"slimlog/format.h\"", "public" ] },
+    #{ include: [ "\"format.h\"", "private", "\"slimlog/format.h\"", "public" ] },
 ]
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1fe2d89..c9e1a03 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -63,7 +63,7 @@ if(ENABLE_FORMATTERS)
     add_code_format_targets(
         CHECK_TARGET formatcheck
         FORMAT_TARGET format
-        SOURCE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}
+        SOURCE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/include ${CMAKE_CURRENT_SOURCE_DIR}/src
         EXCLUDE_DIRS ${CMAKE_BINARY_DIR}
     )
 endif()
@@ -80,7 +80,7 @@ if(ENABLE_ANALYZERS)
     set(CPPCHECK_MIN_VERSION 2.10)
     set(CLANG_TIDY_MIN_VERSION 17.0)
     set(CLANG_FORMAT_MIN_VERSION 17.0)
-    set(IWYU_MIN_VERSION 0.21)
+    set(IWYU_MIN_VERSION 0.23)
     include(StaticCodeAnalysis)
     enable_static_code_analysis(
         CLANG_TIDY_EXTRA_ARGS -header-filter=.*
diff --git a/include/slimlog/format-inl.h b/include/slimlog/format-inl.h
index c413978..3b6d9c5 100644
--- a/include/slimlog/format-inl.h
+++ b/include/slimlog/format-inl.h
@@ -15,6 +15,7 @@
 #else
 #include <fmt/core.h>
 #endif
+#include <chrono>
 #else
 #include <array>
 #endif
diff --git a/include/slimlog/format.h b/include/slimlog/format.h
index 3074694..7e0ba19 100644
--- a/include/slimlog/format.h
+++ b/include/slimlog/format.h
@@ -22,7 +22,6 @@
 #include <format>
 #endif
 
-#include <chrono>
 #include <concepts>
 #include <cstring>
 #include <iterator>
diff --git a/include/slimlog/logger.h b/include/slimlog/logger.h
index 6e6fd0b..28c71e9 100644
--- a/include/slimlog/logger.h
+++ b/include/slimlog/logger.h
@@ -139,7 +139,7 @@ class Logger {
      * @return Shared pointer to the created sink.
      */
     template<
-        template<typename, typename, std::size_t, typename>
+        template<typename, typename, std::size_t, typename> // For clang-format < 19
         typename T,
         std::size_t SinkBufferSize = DefaultBufferSize,
         typename SinkAllocator = Allocator,
diff --git a/include/slimlog/pattern-inl.h b/include/slimlog/pattern-inl.h
index a86c492..c8ed5cf 100644
--- a/include/slimlog/pattern-inl.h
+++ b/include/slimlog/pattern-inl.h
@@ -16,6 +16,7 @@
 #include <functional>
 #include <iterator>
 #include <limits>
+#include <variant>
 
 namespace SlimLog {
 
@@ -262,8 +263,10 @@ void Pattern<Char>::format_generic(auto& out, const auto& item, T data)
 }
 
 template<typename Char>
-constexpr auto Pattern<Char>::parse_nonnegative_int(
-    const Char*& begin, const Char* end, int error_value) noexcept -> int
+constexpr auto Pattern<Char>::parse_nonnegative_int( // For clang-format < 19
+    const Char*& begin,
+    const Char* end,
+    int error_value) noexcept -> int
 {
     unsigned value = 0;
     unsigned prev = 0;
@@ -291,8 +294,10 @@ constexpr auto Pattern<Char>::parse_nonnegative_int(
 }
 
 template<typename Char>
-constexpr auto Pattern<Char>::parse_align(
-    const Char* begin, const Char* end, Placeholder::StringSpecs& specs) -> const Char*
+constexpr auto Pattern<Char>::parse_align( // For clang-format < 19
+    const Char* begin,
+    const Char* end,
+    Placeholder::StringSpecs& specs) -> const Char*
 {
     auto align = Placeholder::StringSpecs::Align::None;
     auto* ptr = std::next(begin, Util::Unicode::code_point_length(begin));
diff --git a/include/slimlog/sink-inl.h b/include/slimlog/sink-inl.h
index d515893..5d308bd 100644
--- a/include/slimlog/sink-inl.h
+++ b/include/slimlog/sink-inl.h
@@ -10,11 +10,7 @@
 #include "slimlog/sink.h" // IWYU pragma: associated
 #include "slimlog/util/os.h"
 
-#ifndef SLIMLOG_HEADER_ONLY
-#include "slimlog/logger.h"
-#endif
-
-#include <algorithm> // IWYU pragma: keep
+#include <algorithm>
 #include <iterator>
 #include <tuple>
 
diff --git a/include/slimlog/sink.h b/include/slimlog/sink.h
index 7b3a8d2..635b5a4 100644
--- a/include/slimlog/sink.h
+++ b/include/slimlog/sink.h
@@ -9,7 +9,6 @@
 #include "slimlog/level.h"
 #include "slimlog/location.h"
 #include "slimlog/pattern.h"
-#include "slimlog/policy.h"
 #include "slimlog/record.h"
 #include "slimlog/util/types.h"
 
@@ -169,7 +168,9 @@ class FormattableSink : public Sink<String, Char> {
 template<class T>
 concept IsFormattableSink = requires(const T& arg) {
     []<typename String, typename Char, std::size_t BufferSize, typename Allocator>(
-        const FormattableSink<String, Char, BufferSize, Allocator>&) {}(arg);
+        const FormattableSink<String, Char, BufferSize, Allocator>&) {
+        /* For clang-format < 19 */
+    }(arg);
 };
 
 /**
@@ -375,7 +376,7 @@ class SinkDriver final {
      * @param location The source code location where the log record is created.
      * @return A new log record of type `RecordType`.
      */
-    static auto
+    static auto // For clang-format < 19
     create_record(Level level, StringViewType category, Location location) -> RecordType;
 
 private:
diff --git a/include/slimlog/sinks/null_sink.h b/include/slimlog/sinks/null_sink.h
index cc6a305..be777cf 100644
--- a/include/slimlog/sinks/null_sink.h
+++ b/include/slimlog/sinks/null_sink.h
@@ -8,7 +8,6 @@
 #include "slimlog/sink.h"
 #include "slimlog/util/types.h"
 
-#include <string_view>
 #include <utility>
 
 namespace SlimLog {
diff --git a/include/slimlog/sinks/ostream_sink.h b/include/slimlog/sinks/ostream_sink.h
index 356e26c..6b25818 100644
--- a/include/slimlog/sinks/ostream_sink.h
+++ b/include/slimlog/sinks/ostream_sink.h
@@ -12,7 +12,6 @@
 #include <cstddef>
 #include <memory>
 #include <ostream>
-#include <string_view>
 #include <utility>
 
 namespace SlimLog {
diff --git a/include/slimlog/util/buffer.h b/include/slimlog/util/buffer.h
index 7816f61..54d314f 100644
--- a/include/slimlog/util/buffer.h
+++ b/include/slimlog/util/buffer.h
@@ -5,11 +5,12 @@
 
 #pragma once
 
-#include <algorithm> // IWYU pragma: keep
+#include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <memory>
 #include <type_traits>
+#include <utility>
 
 #ifdef SLIMLOG_FMTLIB
 #if __has_include(<fmt/base.h>)
diff --git a/include/slimlog/util/os.h b/include/slimlog/util/os.h
index bc2d608..6386511 100644
--- a/include/slimlog/util/os.h
+++ b/include/slimlog/util/os.h
@@ -12,10 +12,12 @@
 
 #include <chrono>
 #include <ctime>
-#include <ratio>
 #include <tuple>
 #include <utility>
 
+// Used by <chrono> in C++20
+// IWYU pragma: no_include <ratio>
+
 #ifdef _WIN32
 #ifndef NOMINMAX
 #define NOMINMAX
diff --git a/include/slimlog/util/types.h b/include/slimlog/util/types.h
index c57b767..0758806 100644
--- a/include/slimlog/util/types.h
+++ b/include/slimlog/util/types.h
@@ -6,6 +6,7 @@
 #pragma once
 
 #include <cassert>
+#include <string_view>
 #include <type_traits>
 
 namespace SlimLog::Util::Types {
diff --git a/include/slimlog/util/unicode.h b/include/slimlog/util/unicode.h
index 60731bc..41ef6b6 100644
--- a/include/slimlog/util/unicode.h
+++ b/include/slimlog/util/unicode.h
@@ -18,6 +18,7 @@
 #include <iterator>
 #include <limits>
 #include <stdexcept>
+#include <type_traits>
 
 namespace SlimLog::Util::Unicode {