diff --git a/.github/workflows/MacOS_Build.yml b/.github/workflows/MacOS_Build.yml
index 4007e0e9..819d4647 100644
--- a/.github/workflows/MacOS_Build.yml
+++ b/.github/workflows/MacOS_Build.yml
@@ -23,10 +23,13 @@ jobs:
     - name: Fetch submodules
       run: git submodule update --init --recursive
 
+    - name: Install LLVM # MacOS comes with "AppleClang" instead of regular Clang, and it can't build the project because no proper C++20
+      run: brew install llvm
+
     - name: Configure CMake
       # Configure CMake in a 'build' subdirectory. `CMAKE_BUILD_TYPE` is only required if you are using a single-configuration generator such as make.
       # See https://cmake.org/cmake/help/latest/variable/CMAKE_BUILD_TYPE.html?highlight=cmake_build_type
-      run: cmake -B ${{github.workspace}}/build -DCMAKE_BUILD_TYPE=${{env.BUILD_TYPE}}
+      run: cmake -B ${{github.workspace}}/build -DCMAKE_BUILD_TYPE=${{env.BUILD_TYPE}} -DCMAKE_C_COMPILER=/usr/local/opt/llvm/bin/clang -DCMAKE_CXX_COMPILER=/usr/local/opt/llvm/bin/clang++
 
     - name: Build
       # Build your program with the given configuration
diff --git a/include/io_file.hpp b/include/io_file.hpp
index f7eb6a00..cd62cbfb 100644
--- a/include/io_file.hpp
+++ b/include/io_file.hpp
@@ -2,6 +2,7 @@
 #include <cstdint>
 #include <cstdio>
 #include <filesystem>
+#include <optional>
 #include <utility>
 
 #ifdef _MSC_VER
diff --git a/third_party/cryptopp/CMakeLists.txt b/third_party/cryptopp/CMakeLists.txt
index 7c43d487..887e80d2 100644
--- a/third_party/cryptopp/CMakeLists.txt
+++ b/third_party/cryptopp/CMakeLists.txt
@@ -353,31 +353,31 @@ endif ()
 
 if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID STREQUAL "Intel" OR CMAKE_CXX_COMPILER MATCHES "xlC")
 
-  if (CRYPTOPP_AMD64 OR CRYPTOPP_I386 AND FALSE)
+  if (CRYPTOPP_AMD64 OR CRYPTOPP_I386)
     CheckCompileLinkOption("-msse2" CRYPTOPP_IA32_SSE2
-                           "${TEST_PROG_DIR}/test_x86_sse2.cxx")
+                           "${TEST_PROG_DIR}/test_x86_sse2.cpp")
     CheckCompileLinkOption("-mssse3" CRYPTOPP_IA32_SSSE3
-                           "${TEST_PROG_DIR}/test_x86_ssse3.cxx")
+                           "${TEST_PROG_DIR}/test_x86_ssse3.cpp")
     CheckCompileLinkOption("-msse4.1" CRYPTOPP_IA32_SSE41
-                           "${TEST_PROG_DIR}/test_x86_sse41.cxx")
+                           "${TEST_PROG_DIR}/test_x86_sse41.cpp")
     CheckCompileLinkOption("-msse4.2" CRYPTOPP_IA32_SSE42
-                           "${TEST_PROG_DIR}/test_x86_sse42.cxx")
+                           "${TEST_PROG_DIR}/test_x86_sse42.cpp")
     CheckCompileLinkOption("-mssse3 -mpclmul" CRYPTOPP_IA32_CLMUL
-                           "${TEST_PROG_DIR}/test_x86_clmul.cxx")
+                           "${TEST_PROG_DIR}/test_x86_clmul.cpp")
     CheckCompileLinkOption("-msse4.1 -maes" CRYPTOPP_IA32_AES
-                           "${TEST_PROG_DIR}/test_x86_aes.cxx")
+                           "${TEST_PROG_DIR}/test_x86_aes.cpp")
     CheckCompileLinkOption("-mavx" CRYPTOPP_IA32_AVX
-                           "${TEST_PROG_DIR}/test_x86_avx.cxx")
+                           "${TEST_PROG_DIR}/test_x86_avx.cpp")
     CheckCompileLinkOption("-mavx2" CRYPTOPP_IA32_AVX2
-                           "${TEST_PROG_DIR}/test_x86_avx2.cxx")
+                           "${TEST_PROG_DIR}/test_x86_avx2.cpp")
     CheckCompileLinkOption("-msse4.2 -msha" CRYPTOPP_IA32_SHA
-                           "${TEST_PROG_DIR}/test_x86_sha.cxx")
-    if (EXISTS "${TEST_PROG_DIR}/test_asm_mixed.cxx")
+                           "${TEST_PROG_DIR}/test_x86_sha.cpp")
+    if (EXISTS "${TEST_PROG_DIR}/test_asm_mixed.cpp")
       CheckCompileLinkOption("" CRYPTOPP_MIXED_ASM
-                             "${TEST_PROG_DIR}/test_asm_mixed.cxx")
+                             "${TEST_PROG_DIR}/test_asm_mixed.cpp")
     else ()
       CheckCompileLinkOption("" CRYPTOPP_MIXED_ASM
-                             "${TEST_PROG_DIR}/test_mixed_asm.cxx")
+                             "${TEST_PROG_DIR}/test_mixed_asm.cpp")
     endif ()
 
     if (NOT CRYPTOPP_MIXED_ASM)
@@ -398,7 +398,7 @@ if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "GNU
       if (NOT CRYPTOPP_IA32_SSE42 AND NOT CRYPTOPP_DISABLE_SSE4)
         list(APPEND CRYPTOPP_COMPILE_OPTIONS "-DCRYPTOPP_DISABLE_SSE4")
       elseif (CRYPTOPP_IA32_SSE42 AND NOT CRYPTOPP_DISABLE_SSE4)
-        set_source_files_properties(${SRC_DIR}/crc_simd.cpp PROPERTIES COMPILE_FLAGS "-msse4.2")
+        set_source_files_properties(${SRC_DIR}/crc_simd.cpp PROPERTIES COMPILE_FLAGS "-msse4.2 -mcrc32")
         if (NOT CRYPTOPP_IA32_CLMUL AND NOT CRYPTOPP_DISABLE_CLMUL)
           list(APPEND CRYPTOPP_COMPILE_OPTIONS "-DCRYPTOPP_DISABLE_CLMUL")
         elseif (CRYPTOPP_IA32_CLMUL AND NOT CRYPTOPP_DISABLE_CLMUL)