diff --git a/src/indexer.cc b/src/indexer.cc
index 59135710..066fc9f1 100644
--- a/src/indexer.cc
+++ b/src/indexer.cc
@@ -1238,8 +1238,8 @@ Index(SemaManager *manager, WorkingFiles *wfiles, VFS *vfs,
   ok = false;
   // -fparse-all-comments enables documentation in the indexer and in
   // code completion.
-  if (g_config->index.comments > 1)
-    CI->getLangOpts()->CommentOpts.ParseAllComments = true;
+  CI->getLangOpts()->CommentOpts.ParseAllComments = g_config->index.comments > 1;
+  CI->getLangOpts()->RetainCommentsFromSystemHeaders = true;
   std::string buf = wfiles->GetContent(main);
   std::vector<std::unique_ptr<llvm::MemoryBuffer>> Bufs;
   if (buf.size())
diff --git a/src/sema_manager.cc b/src/sema_manager.cc
index 096f2c16..d8e7608e 100644
--- a/src/sema_manager.cc
+++ b/src/sema_manager.cc
@@ -363,6 +363,7 @@ void BuildPreamble(Session &session, CompilerInvocation &CI,
   CI.getDiagnosticOpts().IgnoreWarnings = false;
   CI.getFrontendOpts().SkipFunctionBodies = true;
   CI.getLangOpts()->CommentOpts.ParseAllComments = g_config->index.comments > 1;
+  CI.getLangOpts()->RetainCommentsFromSystemHeaders = true;
 
   StoreDiags DC(task.path);
   IntrusiveRefCntPtr<DiagnosticsEngine> DE =