diff --git a/quic/core/crypto/certificate_view.h b/quic/core/crypto/certificate_view.h
index f2e99ba..7439ee6 100644
--- a/quic/core/crypto/certificate_view.h
+++ b/quic/core/crypto/certificate_view.h
@@ -124,7 +124,8 @@
 };
 
 // Parses a DER-encoded X.509 NameAttribute.  Exposed primarily for testing.
-absl::optional<std::string> X509NameAttributeToString(CBS input);
+QUIC_EXPORT_PRIVATE absl::optional<std::string> X509NameAttributeToString(
+    CBS input);
 
 // Parses a DER time based on the specified ASN.1 tag.  Exposed primarily for
 // testing.