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
+// UNSUPPORTED: c++14, c++17, c++20
 // 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 +8,10 @@
 
 from libcxx.test.dsl import *
 
-_allStandards = ['c++03', 'c++11', 'c++14', 'c++17', 'c++2a', 'c++2b']
+_allStandards = ['c++03', 'c++11', 'c++14', 'c++17', 'c++20', 'c++2b']
+_standardFallback = {'c++11': 'c++0x', 'c++14': 'c++1y', 'c++17': 'c++1z', 'c++20': 'c++2a'}
+_undoStandardFallback = dict((v, k) for k, v in _standardFallback.items())
+_allStandardsAndFallbacks = _allStandards + list(_standardFallback.values())
 _warningFlags = [
   '-Werror',
   '-Wall',
@@ -38,13 +41,25 @@
   '-Wno-unused-local-typedef',
 ]
 
+
+def getLatestStdFlag(cfg):
+  for s in reversed(_allStandards):
+    if hasCompileFlag(cfg, '-std='+s):
+      return s
+    if s in _standardFallback:
+      fs = _standardFallback[s]
+      if hasCompileFlag(cfg, '-std='+fs):
+        return fs
+  return _allStandards[0]
+
+
 DEFAULT_PARAMETERS = [
   # Core parameters of the test suite
-  Parameter(name='std', choices=_allStandards, type=str,
+  Parameter(name='std', choices=_allStandardsAndFallbacks, 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: getLatestStdFlag(cfg),
             actions=lambda std: [
-              AddFeature(std),
+              AddFeature(_undoStandardFallback[std] if std in _undoStandardFallback else std),
               AddCompileFlag('-std={}'.format(std)),
             ]),