diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -564,6 +564,12 @@
         S.SymInfo.Lang = index::SymbolLanguage::C;
         S.Origin = Opts.Origin;
         S.CanonicalDeclaration = R.Location;
+        // Make the macro visible for code completion if main file is an
+        // include-able header.
+        if (!HeaderFileURIs->getIncludeHeader(SM.getMainFileID()).empty()) {
+          S.Flags |= Symbol::IndexedForCodeCompletion;
+          S.Flags |= Symbol::VisibleOutsideFile;
+        }
         Symbols.insert(S);
       }
     }
diff --git a/clang-tools-extra/clangd/unittests/FileIndexTests.cpp b/clang-tools-extra/clangd/unittests/FileIndexTests.cpp
--- a/clang-tools-extra/clangd/unittests/FileIndexTests.cpp
+++ b/clang-tools-extra/clangd/unittests/FileIndexTests.cpp
@@ -727,6 +727,19 @@
   EXPECT_THAT(MT.child("f3").children(), ElementsAre(Pair("relations", _)));
   EXPECT_THAT(MT.child("f3").total(), Gt(0U));
 }
+
+TEST(FileIndexTest, MacrosFromMainFile) {
+  FileIndex Idx;
+  TestTU TU;
+  TU.Code = "#pragma once\n#define FOO";
+  TU.Filename = "foo.h";
+  auto AST = TU.build();
+  Idx.updateMain(testPath(TU.Filename), AST);
+
+  auto &FooSymbol = findSymbol(runFuzzyFind(Idx, ""), "FOO");
+  EXPECT_TRUE(FooSymbol.Flags & Symbol::IndexedForCodeCompletion);
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang