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
@@ -552,6 +552,8 @@
           # v15.8.8. Re-evaluate the usefulness of this diagnostic when the bug
           # is fixed.
       -wd4709 # Suppress comma operator within array index expression
+      -wd4129 # Suppress ''character' : unrecognized character escape sequence'
+          # warning, because MSVC also warns about them in raw string  literals.
 
       # Ideally, we'd like this warning to be enabled, but even MSVC 2019 doesn't
       # support the 'aligned' attribute in the way that clang sources requires (for