diff --git a/clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp b/clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp
--- a/clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp
+++ b/clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp
@@ -1490,6 +1490,29 @@
   EXPECT_THAT(Symbols, Contains(QName("operator delete")));
 }
 
+TEST_F(SymbolCollectorTest, UndefOfModuleMacro) {
+  auto TU = TestTU::withCode(R"cpp(#include "/bar.h")cpp");
+  TU.AdditionalFiles["/bar.h"] = R"cpp(
+    #include "/foo.h"
+    #undef X
+    )cpp";
+  TU.AdditionalFiles["/foo.h"] = "#define X 1";
+  TU.AdditionalFiles["/module.map"] = R"cpp(
+    module foo {
+     header "/foo.h"
+     export *
+   }
+   )cpp";
+  TU.ExtraArgs.push_back("-fmodules");
+  TU.ExtraArgs.push_back("-fmodule-map-file=/module.map");
+  TU.OverlayRealFileSystem = true;
+
+  TU.build();
+  EXPECT_THAT(
+      TU.headerSymbols(),
+      Contains(AllOf(QName("X"), DeclURI(URI::create("/foo.h").toString()))));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang
diff --git a/clang-tools-extra/clangd/unittests/TestTU.h b/clang-tools-extra/clangd/unittests/TestTU.h
--- a/clang-tools-extra/clangd/unittests/TestTU.h
+++ b/clang-tools-extra/clangd/unittests/TestTU.h
@@ -65,6 +65,10 @@
   // Simulate a header guard of the header (using an #import directive).
   bool ImplicitHeaderGuard = true;
 
+  // Whether to use overlay the TestFS over the real filesystem. This is
+  // required for use of modules.
+  bool OverlayRealFileSystem = false;
+
   // By default, build() will report Error diagnostics as GTest errors.
   // Suppress this behavior by adding an 'error-ok' comment to the code.
   ParsedAST build() const;
diff --git a/clang-tools-extra/clangd/unittests/TestTU.cpp b/clang-tools-extra/clangd/unittests/TestTU.cpp
--- a/clang-tools-extra/clangd/unittests/TestTU.cpp
+++ b/clang-tools-extra/clangd/unittests/TestTU.cpp
@@ -54,7 +54,14 @@
   Inputs.CompileCommand.Filename = FullFilename;
   Inputs.CompileCommand.Directory = testRoot();
   Inputs.Contents = Code;
-  Inputs.FS = buildTestFS(Files);
+  if (OverlayRealFileSystem) {
+    IntrusiveRefCntPtr<llvm::vfs::OverlayFileSystem> OverlayFileSystem =
+        new llvm::vfs::OverlayFileSystem(llvm::vfs::getRealFileSystem());
+    OverlayFileSystem->pushOverlay(buildTestFS(Files));
+    Inputs.FS = OverlayFileSystem;
+  } else {
+    Inputs.FS = buildTestFS(Files);
+  }
   Inputs.Opts = ParseOptions();
   Inputs.Opts.BuildRecoveryAST = true;
   Inputs.Opts.PreserveRecoveryASTType = true;
diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -1115,6 +1115,28 @@
     return nullptr;
   }
 
+  // Returns MacroInfo for the latest definition of II within a module, nullptr
+  // if this macro was never defined in a module. The return MacroInfo may refer
+  // to definition that was overridden locally.
+  MacroInfo *getMacroInfoFromModules(const IdentifierInfo *II) {
+    if (!II->hasMacroDefinition())
+      return nullptr;
+    MacroState &S = CurSubmoduleState->Macros[II];
+    auto ActiveModuleMacros = S.getActiveModuleMacros(*this, II);
+    for (auto MM = ActiveModuleMacros.rbegin(); MM != ActiveModuleMacros.rend();
+         MM++) {
+      if (auto *MI = (*MM)->getMacroInfo())
+        return MI;
+    }
+    auto OverriddenMacros = S.getOverriddenMacros();
+    for (auto MM = OverriddenMacros.rbegin(); MM != OverriddenMacros.rend();
+         MM++) {
+      if (auto *MI = (*MM)->getMacroInfo())
+        return MI;
+    }
+    return nullptr;
+  }
+
   /// Given an identifier, return the latest non-imported macro
   /// directive for that identifier.
   ///
diff --git a/clang/lib/Index/IndexingAction.cpp b/clang/lib/Index/IndexingAction.cpp
--- a/clang/lib/Index/IndexingAction.cpp
+++ b/clang/lib/Index/IndexingAction.cpp
@@ -147,14 +147,24 @@
   Unit.visitLocalTopLevelDecls(&IndexCtx, topLevelDeclVisitor);
 }
 
-static void indexPreprocessorMacros(const Preprocessor &PP,
+static void indexPreprocessorMacros(Preprocessor &PP,
                                     IndexDataConsumer &DataConsumer) {
-  for (const auto &M : PP.macros())
-    if (MacroDirective *MD = M.second.getLatest())
+  for (const auto &M : PP.macros()) {
+    if (MacroDirective *MD = M.second.getLatest()) {
+      auto *MI = MD->getMacroInfo();
+      if (!MI) {
+        // It is possible for MI to be nullptr if we our translation unit had
+        // only #undef of a macro defined in a module. In that case, dig deeper
+        // and use the definition from the module to yield the same indexing
+        // result whether we are using modules or not.
+        MI = PP.getMacroInfoFromModules(M.first);
+      }
+
       DataConsumer.handleMacroOccurrence(
-          M.first, MD->getMacroInfo(),
-          static_cast<unsigned>(index::SymbolRole::Definition),
+          M.first, MI, static_cast<unsigned>(index::SymbolRole::Definition),
           MD->getLocation());
+    }
+  }
 }
 
 void index::indexASTUnit(ASTUnit &Unit, IndexDataConsumer &DataConsumer,