diff --git a/clang-tools-extra/clangd/Preamble.cpp b/clang-tools-extra/clangd/Preamble.cpp
--- a/clang-tools-extra/clangd/Preamble.cpp
+++ b/clang-tools-extra/clangd/Preamble.cpp
@@ -459,7 +459,8 @@
   bool IncludesChanged = BaselineScan->Includes != ModifiedScan->Includes;
   bool DirectivesChanged =
       BaselineScan->TextualDirectives != ModifiedScan->TextualDirectives;
-  if (!IncludesChanged && !DirectivesChanged)
+  if ((PatchType == PatchType::MacroDirectives || !IncludesChanged) &&
+      !DirectivesChanged)
     return PreamblePatch::unmodified(Baseline);
 
   PreamblePatch PP;
diff --git a/clang-tools-extra/clangd/unittests/PreambleTests.cpp b/clang-tools-extra/clangd/unittests/PreambleTests.cpp
--- a/clang-tools-extra/clangd/unittests/PreambleTests.cpp
+++ b/clang-tools-extra/clangd/unittests/PreambleTests.cpp
@@ -554,6 +554,20 @@
   auto AST = createPatchedAST(Baseline, Modified);
   ASSERT_TRUE(AST);
 }
+
+TEST(PreamblePatch, NoopWhenNotRequested) {
+  llvm::StringLiteral Baseline = "#define M\nint num = M;";
+  llvm::StringLiteral Modified = "#define M\n#include <foo.h>\nint num = M;";
+  auto TU = TestTU::withCode(Baseline);
+  auto BaselinePreamble = TU.preamble();
+  ASSERT_TRUE(BaselinePreamble);
+
+  TU.Code = Modified.str();
+  MockFS FS;
+  auto PP = PreamblePatch::createMacroPatch(testPath(TU.Filename),
+                                            TU.inputs(FS), *BaselinePreamble);
+  EXPECT_TRUE(PP.text().empty());
+}
 } // namespace
 } // namespace clangd
 } // namespace clang