diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -592,6 +592,7 @@
       -Wno-user-defined-literals
       -Wno-covered-switch-default
       -Wno-suggest-override
+      -Wno-ctad-maybe-unsupported
     )
     if (LIBCXX_TARGETING_CLANG_CL)
       target_add_compile_flags_if_supported(${target} PRIVATE
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -794,6 +794,9 @@
 
   # Prevent bugs that can happen with llvm's brace style.
   add_flag_if_supported("-Wmisleading-indentation" MISLEADING_INDENTATION_FLAG)
+
+  # Enable -Wctad-maybe-unsupported to catch unintended use of CTAD.
+  add_flag_if_supported("-Wctad-maybe-unsupported" CTAD_MAYBE_UNSPPORTED_FLAG)
 endif (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
 
 if (LLVM_COMPILER_IS_GCC_COMPATIBLE AND NOT LLVM_ENABLE_WARNINGS)
diff --git a/llvm/include/llvm/CodeGen/RDFGraph.h b/llvm/include/llvm/CodeGen/RDFGraph.h
--- a/llvm/include/llvm/CodeGen/RDFGraph.h
+++ b/llvm/include/llvm/CodeGen/RDFGraph.h
@@ -934,6 +934,8 @@
     const DataFlowGraph &G;
   };
 
+  template <typename T> Print(const T &, const DataFlowGraph &) -> Print<T>;
+
   template <typename T>
   struct PrintNode : Print<NodeAddr<T>> {
     PrintNode(const NodeAddr<T> &x, const DataFlowGraph &g)