diff --git a/flang/lib/Decimal/CMakeLists.txt b/flang/lib/Decimal/CMakeLists.txt
--- a/flang/lib/Decimal/CMakeLists.txt
+++ b/flang/lib/Decimal/CMakeLists.txt
@@ -1,3 +1,40 @@
+if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  cmake_minimum_required(VERSION 3.13.4)
+
+  project(FortranDecimal C CXX)
+
+  set(CMAKE_CXX_STANDARD 17)
+  set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
+  set(CMAKE_CXX_EXTENSIONS OFF)
+
+  set(FLANG_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../..")
+
+  set(LLVM_COMMON_CMAKE_UTILS "${FLANG_SOURCE_DIR}/../cmake")
+  set(LLVM_CMAKE_UTILS "${FLANG_SOURCE_DIR}/../llvm/cmake")
+
+  # Add path for custom modules
+  list(INSERT CMAKE_MODULE_PATH 0
+    "${FLANG_SOURCE_DIR}/cmake"
+    "${FLANG_SOURCE_DIR}/cmake/modules"
+    "${LLVM_COMMON_CMAKE_UTILS}"
+    "${LLVM_COMMON_CMAKE_UTILS}/Modules"
+    "${LLVM_CMAKE_UTILS}"
+    "${LLVM_CMAKE_UTILS}/modules"
+    )
+
+  include(AddLLVM)
+  include(AddFlang)
+
+  include(TestBigEndian)
+  test_big_endian(IS_BIGENDIAN)
+  if (IS_BIGENDIAN)
+    add_compile_definitions(FLANG_BIG_ENDIAN=1)
+  else ()
+    add_compile_definitions(FLANG_LITTLE_ENDIAN=1)
+  endif ()
+  include_directories(BEFORE
+    ${FLANG_SOURCE_DIR}/include)
+endif()
 
 add_flang_library(FortranDecimal INSTALL_WITH_TOOLCHAIN
   binary-to-decimal.cpp
diff --git a/flang/runtime/CMakeLists.txt b/flang/runtime/CMakeLists.txt
--- a/flang/runtime/CMakeLists.txt
+++ b/flang/runtime/CMakeLists.txt
@@ -6,6 +6,44 @@
 #
 #===------------------------------------------------------------------------===#
 
+if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  cmake_minimum_required(VERSION 3.13.4)
+
+  project(FlangRuntime C CXX)
+
+  set(CMAKE_CXX_STANDARD 17)
+  set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
+  set(CMAKE_CXX_EXTENSIONS OFF)
+
+  set(FLANG_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/..")
+
+  set(LLVM_COMMON_CMAKE_UTILS "${FLANG_SOURCE_DIR}/../cmake")
+  set(LLVM_CMAKE_UTILS "${FLANG_SOURCE_DIR}/../llvm/cmake")
+
+  # Add path for custom modules
+  list(INSERT CMAKE_MODULE_PATH 0
+    "${FLANG_SOURCE_DIR}/cmake"
+    "${FLANG_SOURCE_DIR}/cmake/modules"
+    "${LLVM_COMMON_CMAKE_UTILS}"
+    "${LLVM_COMMON_CMAKE_UTILS}/Modules"
+    "${LLVM_CMAKE_UTILS}"
+    "${LLVM_CMAKE_UTILS}/modules"
+    )
+
+  include(AddLLVM)
+  include(AddFlang)
+
+  include(TestBigEndian)
+  test_big_endian(IS_BIGENDIAN)
+  if (IS_BIGENDIAN)
+    add_compile_definitions(FLANG_BIG_ENDIAN=1)
+  else ()
+    add_compile_definitions(FLANG_LITTLE_ENDIAN=1)
+  endif ()
+  include_directories(BEFORE
+    ${FLANG_SOURCE_DIR}/include)
+endif()
+
 include(CheckCXXSymbolExists)
 include(CheckCXXSourceCompiles)
 check_cxx_symbol_exists(strerror string.h HAVE_STRERROR)