diff --git a/quic/core/tls_client_handshaker.h b/quic/core/tls_client_handshaker.h
index d8d8499..d2d0a4a 100644
--- a/quic/core/tls_client_handshaker.h
+++ b/quic/core/tls_client_handshaker.h
@@ -123,7 +123,7 @@
 
 // Allows tests to override the ALPN used by clients.
 // DO NOT use outside of tests.
-extern std::string* quic_alpn_override_on_client_for_tests;
+QUIC_EXPORT_PRIVATE extern std::string* quic_alpn_override_on_client_for_tests;
 
 }  // namespace quic