diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index d9f6311d9b48e..dd00636fcf0b7 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -1029,8 +1029,10 @@ add_custom_target(generate-cxx-headers ALL DEPENDS ${_all_includes})
 add_library(cxx-headers INTERFACE)
 target_link_libraries(cxx-headers INTERFACE libcxx-abi-headers)
 add_dependencies(cxx-headers generate-cxx-headers)
-target_include_directories(cxx-headers INTERFACE ${LIBCXX_GENERATED_INCLUDE_DIR}
-                                                 ${LIBCXX_GENERATED_INCLUDE_TARGET_DIR})
+# It's important that the arch directory be included first so that its header files
+# which interpose on the default include dir be included instead of the default ones.
+target_include_directories(cxx-headers INTERFACE ${LIBCXX_GENERATED_INCLUDE_TARGET_DIR}
+                                                 ${LIBCXX_GENERATED_INCLUDE_DIR})
 
 if (LIBCXX_INSTALL_HEADERS)
   foreach(file ${files})
diff --git a/libcxx/modules/CMakeLists.txt b/libcxx/modules/CMakeLists.txt
index 338769d64fd40..395226fb37287 100644
--- a/libcxx/modules/CMakeLists.txt
+++ b/libcxx/modules/CMakeLists.txt
@@ -128,8 +128,10 @@ if ("${LIBCXX_GENERATED_INCLUDE_DIR}" STREQUAL "${LIBCXX_GENERATED_INCLUDE_TARGE
   # This typically happens when the target is not installed.
   set(LIBCXX_CONFIGURED_INCLUDE_DIRS "${LIBCXX_GENERATED_INCLUDE_DIR}")
 else()
+  # It's important that the arch directory be included first so that its header files
+  # which interpose on the default include dir be included instead of the default ones.
   set(LIBCXX_CONFIGURED_INCLUDE_DIRS
-    "${LIBCXX_GENERATED_INCLUDE_DIR};${LIBCXX_GENERATED_INCLUDE_TARGET_DIR}"
+    "${LIBCXX_GENERATED_INCLUDE_TARGET_DIR};${LIBCXX_GENERATED_INCLUDE_DIR}"
   )
 endif()
 configure_file(