diff --git a/quiche/binary_http/binary_http_message.h b/quiche/binary_http/binary_http_message.h
index 852df93..70e1dff 100644
--- a/quiche/binary_http/binary_http_message.h
+++ b/quiche/binary_http/binary_http_message.h
@@ -161,7 +161,8 @@
   const ControlData control_data_;
 };
 
-void PrintTo(const BinaryHttpRequest& msg, std::ostream* os);
+void QUICHE_EXPORT_PRIVATE PrintTo(const BinaryHttpRequest& msg,
+                                   std::ostream* os);
 
 class QUICHE_EXPORT_PRIVATE BinaryHttpResponse : public BinaryHttpMessage {
  public:
@@ -258,7 +259,8 @@
   const uint16_t status_code_;
 };
 
-void PrintTo(const BinaryHttpResponse& msg, std::ostream* os);
+void QUICHE_EXPORT_PRIVATE PrintTo(const BinaryHttpResponse& msg,
+                                   std::ostream* os);
 }  // namespace quiche
 
 #endif  // QUICHE_BINARY_HTTP_BINARY_HTTP_MESSAGE_H_