diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -511,11 +511,11 @@
 # Required flags ==============================================================
 function(cxx_add_basic_build_flags target)
 
-  # Require C++17 for all targets. C++17 is needed to use aligned allocation
-  # in the dylib.
+  # Require C++20 for all targets. C++17 is needed to use aligned allocation
+  # in the dylib. C++20 is needed to use char8_t.
   set_target_properties(${target} PROPERTIES
-    CXX_STANDARD 17
-    CXX_STANDARD_REQUIRED YES
+    CXX_STANDARD 20
+    CXX_STANDARD_REQUIRED NO
     CXX_EXTENSIONS NO)
 
   # When building the dylib, don't warn for unavailable aligned allocation
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -174,9 +174,9 @@
                           CXX_EXTENSIONS
                             OFF
                           CXX_STANDARD
-                            17
+                            20
                           CXX_STANDARD_REQUIRED
-                            ON
+                            OFF
                           COMPILE_FLAGS
                             "${LIBCXXABI_COMPILE_FLAGS}"
                           LINK_FLAGS
@@ -241,9 +241,9 @@
                           CXX_EXTENSIONS
                             OFF
                           CXX_STANDARD
-                            17
+                            20
                           CXX_STANDARD_REQUIRED
-                            ON
+                            OFF
                           COMPILE_FLAGS
                             "${LIBCXXABI_COMPILE_FLAGS}"
                           LINK_FLAGS