diff --git a/ssl/internal.h b/ssl/internal.h
index 7a3979b..e1585c3 100644
--- a/ssl/internal.h
+++ b/ssl/internal.h
@@ -2052,6 +2052,9 @@
     SSL_HANDSHAKE *hs, Array<uint8_t> *out,
     enum ssl_cert_verify_context_t cert_verify_context);
 
+// ssl_is_valid_alpn_list returns whether |in| is a valid ALPN protocol list.
+bool ssl_is_valid_alpn_list(Span<const uint8_t> in);
+
 // ssl_is_alpn_protocol_allowed returns whether |protocol| is a valid server
 // selection for |hs->ssl|'s client preferences.
 bool ssl_is_alpn_protocol_allowed(const SSL_HANDSHAKE *hs,