diff --git a/http2/adapter/http2_protocol.h b/http2/adapter/http2_protocol.h
index 0529bd6..d48a9ab 100644
--- a/http2/adapter/http2_protocol.h
+++ b/http2/adapter/http2_protocol.h
@@ -39,7 +39,8 @@
   uint32_t value;
 };
 
-bool operator==(const Http2Setting& a, const Http2Setting& b);
+QUICHE_EXPORT_PRIVATE bool operator==(const Http2Setting& a,
+                                      const Http2Setting& b);
 
 // The maximum possible stream ID.
 const Http2StreamId kMaxStreamId = 0x7FFFFFFF;