diff --git a/libcxx/cmake/caches/Generic-cxx20.cmake b/libcxx/cmake/caches/Generic-cxx20.cmake
--- a/libcxx/cmake/caches/Generic-cxx20.cmake
+++ b/libcxx/cmake/caches/Generic-cxx20.cmake
@@ -1,2 +1,2 @@
-set(LIBCXX_TEST_PARAMS "std=c++2a" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "std=c++20" CACHE STRING "")
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/docs/TestingLibcxx.rst b/libcxx/docs/TestingLibcxx.rst
--- a/libcxx/docs/TestingLibcxx.rst
+++ b/libcxx/docs/TestingLibcxx.rst
@@ -126,7 +126,7 @@
 
 .. option:: std=<standard version>
 
-  **Values**: c++03, c++11, c++14, c++17, c++2a, c++2b
+  **Values**: c++03, c++11, c++14, c++17, c++20, c++2b
 
   Change the standard version used when building the tests.
 
diff --git a/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array11.pass.cpp b/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array11.pass.cpp
--- a/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array11.pass.cpp
+++ b/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array11.pass.cpp
@@ -11,7 +11,7 @@
 // Note that sized delete operator definitions below are simply ignored
 // when sized deallocation is not supported, e.g., prior to C++14.
 
-// UNSUPPORTED: c++14, c++17, c++2a
+// REQUIRES: c++03 || c++11
 // UNSUPPORTED: sanitizer-new-delete
 
 #include <new>
diff --git a/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete11.pass.cpp b/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete11.pass.cpp
--- a/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete11.pass.cpp
+++ b/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete11.pass.cpp
@@ -11,7 +11,7 @@
 // Note that sized delete operator definitions below are simply ignored
 // when sized deallocation is not supported, e.g., prior to C++14.
 
-// UNSUPPORTED: c++14, c++17, c++2a
+// REQUIRES: c++03 || c++11
 // UNSUPPORTED: sanitizer-new-delete
 
 #include <new>
diff --git a/libcxx/test/std/strings/basic.string/string.contains/contains.char.pass.cpp b/libcxx/test/std/strings/basic.string/string.contains/contains.char.pass.cpp
--- a/libcxx/test/std/strings/basic.string/string.contains/contains.char.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.contains/contains.char.pass.cpp
@@ -5,7 +5,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string>
 
diff --git a/libcxx/test/std/strings/basic.string/string.contains/contains.ptr.pass.cpp b/libcxx/test/std/strings/basic.string/string.contains/contains.ptr.pass.cpp
--- a/libcxx/test/std/strings/basic.string/string.contains/contains.ptr.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.contains/contains.ptr.pass.cpp
@@ -5,7 +5,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string>
 
diff --git a/libcxx/test/std/strings/basic.string/string.contains/contains.string_view.pass.cpp b/libcxx/test/std/strings/basic.string/string.contains/contains.string_view.pass.cpp
--- a/libcxx/test/std/strings/basic.string/string.contains/contains.string_view.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.contains/contains.string_view.pass.cpp
@@ -5,7 +5,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string>
 
diff --git a/libcxx/test/std/strings/string.view/string.view.template/contains.char.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/contains.char.pass.cpp
--- a/libcxx/test/std/strings/string.view/string.view.template/contains.char.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/contains.char.pass.cpp
@@ -5,7 +5,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string_view>
 
diff --git a/libcxx/test/std/strings/string.view/string.view.template/contains.ptr.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/contains.ptr.pass.cpp
--- a/libcxx/test/std/strings/string.view/string.view.template/contains.ptr.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/contains.ptr.pass.cpp
@@ -5,7 +5,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string_view>
 
diff --git a/libcxx/test/std/strings/string.view/string.view.template/contains.string_view.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/contains.string_view.pass.cpp
--- a/libcxx/test/std/strings/string.view/string.view.template/contains.string_view.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/contains.string_view.pass.cpp
@@ -5,7 +5,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string_view>
 
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_scoped_enum.pass.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_scoped_enum.pass.cpp
--- a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_scoped_enum.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_scoped_enum.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // type_traits
 
diff --git a/libcxx/test/std/utilities/utility/utility.underlying/to_underlying.pass.cpp b/libcxx/test/std/utilities/utility/utility.underlying/to_underlying.pass.cpp
--- a/libcxx/test/std/utilities/utility/utility.underlying/to_underlying.pass.cpp
+++ b/libcxx/test/std/utilities/utility/utility.underlying/to_underlying.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // [utility.underlying], to_underlying
 // template <class T>
diff --git a/libcxx/test/std/utilities/utility/utility.underlying/to_underlying.verify.cpp b/libcxx/test/std/utilities/utility/utility.underlying/to_underlying.verify.cpp
--- a/libcxx/test/std/utilities/utility/utility.underlying/to_underlying.verify.cpp
+++ b/libcxx/test/std/utilities/utility/utility.underlying/to_underlying.verify.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // [utility.underlying], to_underlying
 // template <class T>
diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
--- a/libcxx/utils/libcxx/test/params.py
+++ b/libcxx/utils/libcxx/test/params.py
@@ -8,7 +8,6 @@
 
 from libcxx.test.dsl import *
 
-_allStandards = ['c++03', 'c++11', 'c++14', 'c++17', 'c++2a', 'c++2b']
 _warningFlags = [
   '-Werror',
   '-Wall',
@@ -38,14 +37,28 @@
   '-Wno-unused-local-typedef',
 ]
 
+_allStandards = ['c++03', 'c++11', 'c++14', 'c++17', 'c++20', 'c++2b']
+def getStdFlag(cfg, std):
+  fallbacks = {
+    'c++11': 'c++0x',
+    'c++14': 'c++1y',
+    'c++17': 'c++1z',
+    'c++20': 'c++2a',
+  }
+  if hasCompileFlag(cfg, '-std='+std):
+    return '-std='+std
+  if fallbacks[std] and hasCompileFlag(cfg, '-std='+fallbacks[std]):
+    return '-std='+fallbacks[std]
+  return None
+
 DEFAULT_PARAMETERS = [
   # Core parameters of the test suite
   Parameter(name='std', choices=_allStandards, type=str,
             help="The version of the standard to compile the test suite with.",
-            default=lambda cfg: next(s for s in reversed(_allStandards) if hasCompileFlag(cfg, '-std='+s)),
+            default=lambda cfg: next(s for s in reversed(_allStandards) if getStdFlag(cfg, s)),
             actions=lambda std: [
               AddFeature(std),
-              AddCompileFlag('-std={}'.format(std)),
+              AddCompileFlag(lambda cfg: getStdFlag(cfg, std)),
             ]),
 
   Parameter(name='enable_exceptions', choices=[True, False], type=bool, default=True,