diff --git a/clang-tools-extra/clangd/ParsedAST.cpp b/clang-tools-extra/clangd/ParsedAST.cpp
--- a/clang-tools-extra/clangd/ParsedAST.cpp
+++ b/clang-tools-extra/clangd/ParsedAST.cpp
@@ -256,6 +256,9 @@
   // Recovery expression currently only works for C++.
   if (CI->getLangOpts()->CPlusPlus)
     CI->getLangOpts()->RecoveryAST = Opts.BuildRecoveryAST;
+  // This is on-by-default in windows to allow parsing SDK headers, but it
+  // breaks many features. Disable it for the main-file (not preamble).
+  CI->getLangOpts()->DelayedTemplateParsing = false;
 
   StoreDiags ASTDiags;
   std::string Content = std::string(Buffer->getBuffer());
diff --git a/clang-tools-extra/clangd/unittests/ParsedASTTests.cpp b/clang-tools-extra/clangd/unittests/ParsedASTTests.cpp
--- a/clang-tools-extra/clangd/unittests/ParsedASTTests.cpp
+++ b/clang-tools-extra/clangd/unittests/ParsedASTTests.cpp
@@ -175,6 +175,17 @@
                         AllOf(DeclNamed("foo"), WithTemplateArgs("<bool>"))}));
 }
 
+TEST(ParsedASTTest, IgnoresDelayedTemplateParsing) {
+  auto TU = TestTU::withCode(R"cpp(
+    template <typename T> void xxx() {
+      int yyy = 0;
+    }
+  )cpp");
+  TU.ExtraArgs.push_back("-fdelayed-template-parsing");
+  auto AST = TU.build();
+  EXPECT_EQ(Decl::Var, findUnqualifiedDecl(AST, "yyy").getKind());
+}
+
 TEST(ParsedASTTest, TokensAfterPreamble) {
   TestTU TU;
   TU.AdditionalFiles["foo.h"] = R"(