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
@@ -56,18 +56,15 @@
 
 
 def getStdFlag(cfg, std):
-    fallbacks = {
-        "c++11": "c++0x",
-        "c++14": "c++1y",
-        "c++17": "c++1z",
-        "c++20": "c++2a",
-        "c++23": "c++2b",
-    }
     # TODO(LLVM-17) Remove this clang-tidy-16 work-around
     if std == "c++23":
         std = "c++2b"
     if hasCompileFlag(cfg, "-std=" + std):
         return "-std=" + std
+    # TODO(LLVM-19) Remove the fallbacks needed for Clang 16.
+    fallbacks = {
+        "c++23": "c++2b",
+    }
     if std in fallbacks and hasCompileFlag(cfg, "-std=" + fallbacks[std]):
         return "-std=" + fallbacks[std]
     return None