Index: clang-tools-extra/clangd/CodeComplete.cpp
===================================================================
--- clang-tools-extra/clangd/CodeComplete.cpp
+++ clang-tools-extra/clangd/CodeComplete.cpp
@@ -1105,14 +1105,19 @@
   ExternalPreprocessorSource *PreambleMacros = PP.getExternalSource();
   // As we have the names of the macros, we can look up their IdentifierInfo
   // and then use this to load just the macros we want.
+  const auto &ITable = PP.getIdentifierTable();
   IdentifierInfoLookup *PreambleIdentifiers =
-      PP.getIdentifierTable().getExternalIdentifierLookup();
+      ITable.getExternalIdentifierLookup();
+
   if (!PreambleIdentifiers || !PreambleMacros)
     return;
-  for (const auto &MacroName : Preamble.Macros.Names)
+  for (const auto &MacroName : Preamble.Macros.Names) {
+    if (ITable.find(MacroName.getKey()) != ITable.end())
+      continue;
     if (auto *II = PreambleIdentifiers->get(MacroName.getKey()))
       if (II->isOutOfDate())
         PreambleMacros->updateOutOfDateIdentifier(*II);
+  }
 }
 
 // Invokes Sema code completion on a file.