diff --git a/quiche/quic/tools/quic_server.h b/quiche/quic/tools/quic_server.h
index 7cb870f..11ff04e 100644
--- a/quiche/quic/tools/quic_server.h
+++ b/quiche/quic/tools/quic_server.h
@@ -35,6 +35,7 @@
 
 class QuicServer : public QuicSpdyServerBase, public QuicSocketEventListener {
  public:
+  // `quic_simple_server_backend` must outlive the created QuicServer.
   QuicServer(std::unique_ptr<ProofSource> proof_source,
              QuicSimpleServerBackend* quic_simple_server_backend);
   QuicServer(std::unique_ptr<ProofSource> proof_source,