Index: clangd/CodeComplete.cpp
===================================================================
--- clangd/CodeComplete.cpp
+++ clangd/CodeComplete.cpp
@@ -702,11 +702,11 @@
     Input.Preamble->CanReuse(*CI, ContentsBuffer.get(), Bounds,
                              Input.VFS.get());
   }
+  // The diagnostic options must be set before creating a CompilerInstance.
+  CI->getDiagnosticOpts().IgnoreWarnings = true;
   auto Clang = prepareCompilerInstance(
       std::move(CI), Input.Preamble, std::move(ContentsBuffer),
       std::move(Input.PCHs), std::move(Input.VFS), DummyDiagsConsumer);
-  auto &DiagOpts = Clang->getDiagnosticOpts();
-  DiagOpts.IgnoreWarnings = true;
 
   // Disable typo correction in Sema.
   Clang->getLangOpts().SpellChecking = false;
Index: clangd/Headers.cpp
===================================================================
--- clangd/Headers.cpp
+++ clangd/Headers.cpp
@@ -71,12 +71,12 @@
   // added more than once.
   CI->getPreprocessorOpts().SingleFileParseMode = true;
 
+  // The diagnostic options must be set before creating a CompilerInstance.
+  CI->getDiagnosticOpts().IgnoreWarnings = true;
   auto Clang = prepareCompilerInstance(
       std::move(CI), /*Preamble=*/nullptr,
       llvm::MemoryBuffer::getMemBuffer(Code, File),
       std::make_shared<PCHContainerOperations>(), FS, IgnoreDiags);
-  auto &DiagOpts = Clang->getDiagnosticOpts();
-  DiagOpts.IgnoreWarnings = true;
 
   if (Clang->getFrontendOpts().Inputs.empty())
     return llvm::make_error<llvm::StringError>(