diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -675,8 +675,6 @@
 endif()
 
 # Assertion flags =============================================================
-define_if(LIBCXX_ENABLE_ASSERTIONS -UNDEBUG)
-define_if_not(LIBCXX_ENABLE_ASSERTIONS -DNDEBUG)
 define_if(LIBCXX_ENABLE_ASSERTIONS -D_LIBCPP_DEBUG=0)
 define_if(LIBCXX_DEBUG_BUILD -D_DEBUG)
 if (LIBCXX_ENABLE_ASSERTIONS AND NOT LIBCXX_DEBUG_BUILD)
diff --git a/libcxx/benchmarks/algorithms.bench.cpp b/libcxx/benchmarks/algorithms.bench.cpp
--- a/libcxx/benchmarks/algorithms.bench.cpp
+++ b/libcxx/benchmarks/algorithms.bench.cpp
@@ -151,7 +151,6 @@
 
 template <class T>
 void sortValues(T& V, Order O) {
-  assert(std::is_sorted(V.begin(), V.end()));
   switch (O) {
   case Order::Random: {
     std::random_device R;