Index: clang-tools-extra/clangd/CodeComplete.cpp
===================================================================
--- clang-tools-extra/clangd/CodeComplete.cpp
+++ clang-tools-extra/clangd/CodeComplete.cpp
@@ -1866,9 +1866,10 @@
              ? std::move(Flow).runWithoutSema(ParseInput.Contents, *Offset,
                                               *ParseInput.TFS)
              : std::move(Flow).run({FileName, *Offset, *Preamble,
-                                    // We want to serve code completions with
-                                    // low latency, so don't bother patching.
-                                    /*PreamblePatch=*/llvm::None, ParseInput});
+                                    /*PreamblePatch=*/
+                                    PreamblePatch::createMacroPatch(
+                                        FileName, ParseInput, *Preamble),
+                                    ParseInput});
 }
 
 SignatureHelp signatureHelp(PathRef FileName, Position Pos,
Index: clang-tools-extra/clangd/Preamble.h
===================================================================
--- clang-tools-extra/clangd/Preamble.h
+++ clang-tools-extra/clangd/Preamble.h
@@ -106,6 +106,9 @@
   static PreamblePatch create(llvm::StringRef FileName,
                               const ParseInputs &Modified,
                               const PreambleData &Baseline);
+  static PreamblePatch createMacroPatch(llvm::StringRef FileName,
+                                        const ParseInputs &Modified,
+                                        const PreambleData &Baseline);
   /// Adjusts CI (which compiles the modified inputs) to be used with the
   /// baseline preamble. This is done by inserting an artifical include to the
   /// \p CI that contains new directives calculated in create.
Index: clang-tools-extra/clangd/Preamble.cpp
===================================================================
--- clang-tools-extra/clangd/Preamble.cpp
+++ clang-tools-extra/clangd/Preamble.cpp
@@ -142,10 +142,11 @@
   unsigned DirectiveLine;
   // Full text that's representing the directive, including the `#`.
   std::string Text;
+  unsigned Offset;
 
   bool operator==(const TextualPPDirective &RHS) const {
-    return std::tie(DirectiveLine, Text) ==
-           std::tie(RHS.DirectiveLine, RHS.Text);
+    return std::tie(DirectiveLine, Text, Offset) ==
+           std::tie(RHS.DirectiveLine, RHS.Text, RHS.Offset);
   }
 };
 
@@ -155,7 +156,7 @@
 std::string spellDirective(llvm::StringRef Prefix,
                            CharSourceRange DirectiveRange,
                            const LangOptions &LangOpts, const SourceManager &SM,
-                           unsigned &DirectiveLine) {
+                           unsigned &DirectiveLine, unsigned &Offset) {
   std::string SpelledDirective;
   llvm::raw_string_ostream OS(SpelledDirective);
   OS << Prefix;
@@ -169,6 +170,7 @@
 
   auto DecompLoc = SM.getDecomposedLoc(DirectiveRange.getBegin());
   DirectiveLine = SM.getLineNumber(DecompLoc.first, DecompLoc.second);
+  Offset = DecompLoc.second;
   auto TargetColumn = SM.getColumnNumber(DecompLoc.first, DecompLoc.second) - 1;
 
   // Pad with spaces before DirectiveRange to make sure it will be on right
@@ -217,7 +219,7 @@
         spellDirective("#define ",
                        CharSourceRange::getTokenRange(
                            MI->getDefinitionLoc(), MI->getDefinitionEndLoc()),
-                       LangOpts, SM, TD.DirectiveLine);
+                       LangOpts, SM, TD.DirectiveLine, TD.Offset);
   }
 
 private:
@@ -528,6 +530,49 @@
   return PP;
 }
 
+PreamblePatch PreamblePatch::createMacroPatch(llvm::StringRef FileName,
+                                              const ParseInputs &Modified,
+                                              const PreambleData &Baseline) {
+
+  auto BaselineScan = scanPreamble(
+      // Contents needs to be null-terminated.
+      Baseline.Preamble.getContents().str(), Modified.CompileCommand);
+  if (!BaselineScan) {
+    elog("Failed to scan baseline of {0}: {1}", FileName,
+         BaselineScan.takeError());
+    return PreamblePatch::unmodified(Baseline);
+  }
+  auto ModifiedScan = scanPreamble(Modified.Contents, Modified.CompileCommand);
+  if (!ModifiedScan) {
+    elog("Failed to scan modified contents of {0}: {1}", FileName,
+         ModifiedScan.takeError());
+    return PreamblePatch::unmodified(Baseline);
+  }
+  PreamblePatch PP;
+  llvm::SmallString<128> PatchName;
+  llvm::sys::path::append(PatchName, llvm::sys::path::parent_path(FileName),
+                          PreamblePatchHeaderName);
+  PP.PatchFileName = PatchName.str().str();
+  PP.ModifiedBounds = ModifiedScan->Bounds;
+
+  llvm::raw_string_ostream Patch(PP.PatchContents);
+  Patch << "#line 0 \"";
+
+  escapeBackslashAndQuotes(FileName, Patch);
+  Patch << "\"\n";
+
+  if (BaselineScan->TextualDirectives != ModifiedScan->TextualDirectives) {
+    for (const auto &TD : ModifiedScan->TextualDirectives) {
+      Patch << "#line " << TD.DirectiveLine << '\n';
+      Patch << TD.Text << '\n';
+    }
+    dlog("Created macro only preamble patch: {0}", Patch.str());
+    Patch.flush();
+    return PP;
+  }
+  return PreamblePatch::unmodified(Baseline);
+}
+
 void PreamblePatch::apply(CompilerInvocation &CI) const {
   // No need to map an empty file.
   if (PatchContents.empty())
Index: clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
===================================================================
--- clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
+++ clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
@@ -3260,6 +3260,23 @@
     EXPECT_THAT(Results.Completions, UnorderedElementsAre(Labeled("BarExt")));
   }
 }
+
+TEST(CompletionTest, PreambleCodeComplete) {
+  llvm::StringLiteral Baseline = "\n#define MACRO 12\nint num = MACRO;";
+  llvm::StringLiteral ModifiedCC =
+      "#include \"header.h\"\n#define MACRO 12\nint num = MACRO; int num2 = M^";
+
+  Annotations Test(ModifiedCC);
+  auto BaselineTU = TestTU::withCode(Baseline);
+  auto ModifiedTU = TestTU::withCode(Test.code());
+
+  MockFS FS;
+  auto Inputs = ModifiedTU.inputs(FS);
+  auto Result = codeComplete(testPath(ModifiedTU.Filename), Test.point(),
+                             BaselineTU.preamble().get(), Inputs, {});
+  EXPECT_THAT(Result.Completions, Not(testing::IsEmpty()));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang
Index: clang-tools-extra/clangd/unittests/PreambleTests.cpp
===================================================================
--- clang-tools-extra/clangd/unittests/PreambleTests.cpp
+++ clang-tools-extra/clangd/unittests/PreambleTests.cpp
@@ -546,6 +546,13 @@
   // Ensure they are dropeed when a patched preamble is used.
   EXPECT_FALSE(createPatchedAST("", Code)->getDiagnostics());
 }
+
+TEST(PreamblePatch, MacroLoc) {
+  llvm::StringLiteral Baseline = "\n#define MACRO 12\nint num = MACRO;";
+  llvm::StringLiteral Modified = " \n#define MACRO 12\nint num = MACRO;";
+  auto AST = createPatchedAST(Baseline, Modified);
+  ASSERT_TRUE(AST);
+}
 } // namespace
 } // namespace clangd
 } // namespace clang