diff --git a/quic/core/crypto/tls_connection.h b/quic/core/crypto/tls_connection.h
index 4774ba6..fd4f64b 100644
--- a/quic/core/crypto/tls_connection.h
+++ b/quic/core/crypto/tls_connection.h
@@ -26,7 +26,7 @@
  public:
   // A TlsConnection::Delegate implements the methods that are set as callbacks
   // of TlsConnection.
-  class Delegate {
+  class QUIC_EXPORT_PRIVATE Delegate {
    public:
     virtual ~Delegate() {}