diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -477,10 +477,6 @@
 # Prevent libc++abi from having library dependencies on libc++
 add_definitions(-D_LIBCPP_DISABLE_EXTERN_TEMPLATE)
 
-# Bring back `std::unexpected`, which is removed in C++17, to support
-# pre-C++17.
-add_definitions(-D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS)
-
 if (MSVC)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)
 endif()