diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 89337964..4d21087d 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -17,19 +17,21 @@ env:
 jobs:
   build-linux:
     runs-on: ubuntu-latest
+    # libc++/libc++abi are not prerequsite libraries but specifies to test CXXFLAGS/LDFLAGS are functional
     env:
       CC: clang
       CXX: clang++
+      CXXFLAGS: -stdlib=libc++
+      LDFLAGS: -lc++abi
     steps:
       - name: checkout
         uses: actions/checkout@v3
         with:
           submodules: recursive
+      # Assumes clang/cmake/libc++/libc++abi are installed on GitHub Actions Runner
       - name: setup prerequisite packages
         run: |
           sudo apt-get update && sudo apt-get install -y \
-            clang \
-            cmake \
             libasound-dev \
             libgtk-3-dev \
             libglu1-mesa-dev \
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 04b0a63a..d072531d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -210,6 +210,11 @@ function(nanoem_cmake_bootstrap _project_name_prefix _build_type)
     set(nanoem_cxxflags "${nanoem_cxxflags} ${CMAKE_CXX_FLAGS_UBSAN}")
     set(nanoem_exe_linker_flags "${nanoem_exe_linker_flags} ${CMAKE_EXE_LINKER_FLAGS_UBSAN}")
     set(nanoem_shared_linker_flags "${nanoem_shared_linker_flags} ${CMAKE_SHARED_LINKER_FLAGS_UBSAN}")
+  else()
+    set(nanoem_cflags "${nanoem_cflags} ${CMAKE_C_FLAGS}")
+    set(nanoem_cxxflags "${nanoem_cxxflags} ${CMAKE_CXX_FLAGS}")
+    set(nanoem_exe_linker_flags "${nanoem_exe_linker_flags} ${CMAKE_EXE_LINKER_FLAGS}")
+    set(nanoem_shared_linker_flags "${nanoem_shared_linker_flags} ${CMAKE_SHARED_LINKER_FLAGS}")
   endif()
   if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
     set(nanoem_cflags "${nanoem_cflags} -std=c++14")
diff --git a/nanoem/CMakeLists.txt b/nanoem/CMakeLists.txt
index a04615fe..1a2efda0 100644
--- a/nanoem/CMakeLists.txt
+++ b/nanoem/CMakeLists.txt
@@ -56,10 +56,6 @@ endif()
 
 # Bullet Physics for optional nanoem prerequisite
 if(NANOEM_ENABLE_BULLET)
-  set(__CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ${CMAKE_FIND_ROOT_PATH_MODE_INCLUDE})
-  set(__CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ${CMAKE_FIND_ROOT_PATH_MODE_LIBRARY})
-  set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE NEVER)
-  set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY NEVER)
   nanoem_cmake_get_install_path("bullet3" BULLET_BASE_PATH BULLET_INSTALL_PATH_DEBUG BULLET_INSTALL_PATH_RELEASE)
   find_path(BULLET_INCLUDE_DIR NAMES btBulletCollisionCommon.h PATH_SUFFIXES include/bullet include PATHS ${BULLET_INSTALL_PATH_RELEASE} NO_DEFAULT_PATH)
   find_library(BULLET_COLLISION_LIBRARY_DEBUG NAMES BulletCollision PATH_SUFFIXES lib PATHS ${BULLET_INSTALL_PATH_DEBUG} NO_DEFAULT_PATH)
@@ -85,8 +81,6 @@ if(NANOEM_ENABLE_BULLET)
                                     $<$<NOT:$<CONFIG:DEBUG>>:${BULLET_DYNAMICS_LIBRARY_RELEASE}>
                                     $<$<NOT:$<CONFIG:DEBUG>>:${BULLET_COLLISION_LIBRARY_RELEASE}>
                                     $<$<NOT:$<CONFIG:DEBUG>>:${BULLET_LINEAR_MATH_LIBRARY_RELEASE}>)
-  set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ${__CMAKE_FIND_ROOT_PATH_MODE_INCLUDE})
-  set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ${__CMAKE_FIND_ROOT_PATH_MODE_LIBRARY})
   message(STATUS "[nanoem] bullet is located at ${BULLET_BASE_PATH}")
   message(STATUS "[nanoem] physics simulation using bullet extension is enabled")
 endif()
diff --git a/scripts/build.cmake b/scripts/build.cmake
index 7aebc11d..c5d38d97 100644
--- a/scripts/build.cmake
+++ b/scripts/build.cmake
@@ -8,6 +8,19 @@ else()
   set(_make_flags -j1)
 endif()
 
+function(get_compiler_flags _cflags _cxxflags)
+  set(_inner_cflags "-std=c99")
+  if(DEFINED ENV{CFLAGS})
+    set(_inner_cflags "${_inner_cflags} $ENV{CFLAGS}")
+  endif()
+  set(_inner_cxxflags "-std=c++14")
+  if(DEFINED ENV{CXXFLAGS})
+    set(_inner_cxxflags "${_inner_cxxflags} $ENV{CXXFLAGS}")
+  endif()
+  set(${_cflags} ${_inner_cflags} PARENT_SCOPE)
+  set(${_cxxflags} ${_inner_cxxflags} PARENT_SCOPE)
+endfunction()
+
 function(rewrite_ninja_ub_workaround _build_path)
   if(EXISTS ${_build_path}/build.ninja)
     file(STRINGS ${_build_path}/build.ninja input_ninja NEWLINE_CONSUME)
@@ -390,8 +403,7 @@ function(compile_icu4c _cmake_build_type _generator _toolset_option _arch_option
       set(_build_flags "${_build_flags} -O2")
       set(_configure_flags --enable-release)
     endif()
-    set(_cflags "${_build_flags} -std=c99")
-    set(_cxxflags "${_build_flags} -std=c++11")
+    get_compiler_flags(_cflags _cxxflags)
     # see https://unicode-org.github.io/icu/userguide/icu_data/buildtool.html#icu-data-configuration-file for more details of ICU_DATA_FILTER_FILE
     execute_process(COMMAND
       ${CMAKE_COMMAND} -E env
@@ -706,21 +718,26 @@ foreach(arch_item ${ARCH_LIST})
       set(global_cmake_flags "${_gcc_flags}")
     endif()
   else()
+    get_compiler_flags(_cflags _cxxflags)
     if(NOT target_generator)
       set(target_generator "Ninja")
     endif()
     if(target_compiler)
-      set(global_cmake_flags "-DCMAKE_CXX_FLAGS='-std=c++14'")
+      list(APPEND _compiler_flags "-DCMAKE_C_FLAGS='${_cflags}'")
+      list(APPEND _compiler_flags "-DCMAKE_CXX_FLAGS='${_cxxflags}'")
+      set(global_cmake_flags "${_compiler_flags}")
     else()
       if(APPLE)
         set(target_compiler "clang")
-        list(APPEND _clang_flags "-DCMAKE_C_FLAGS='-std=c99'")
-        list(APPEND _clang_flags "-DCMAKE_CXX_FLAGS='-std=c++14'")
+        list(APPEND _clang_flags "-DCMAKE_C_FLAGS='${_cflags}'")
+        list(APPEND _clang_flags "-DCMAKE_CXX_FLAGS='${_cxxflags}'")
         set(global_cmake_flags "${_clang_flags}")
       else()
         set(target_compiler "gcc")
-        list(APPEND _gcc_flags "-DCMAKE_C_FLAGS='-std=c99 -fPIC'")
-        list(APPEND _gcc_flags "-DCMAKE_CXX_FLAGS='-std=c++14 -fPIC'")
+        set(_cflags "${_cflags} -fPIC")
+        set(_cflags "${_cxxflags} -fPIC")
+        list(APPEND _gcc_flags "-DCMAKE_C_FLAGS='${_cflags}'")
+        list(APPEND _gcc_flags "-DCMAKE_CXX_FLAGS='${_cxxflags}'")
         set(global_cmake_flags "${_gcc_flags}")
       endif()
     endif()