diff --git a/quic/core/proto/crypto_server_config.proto b/quic/core/proto/crypto_server_config.proto
index 06db4a7..bb447dc 100644
--- a/quic/core/proto/crypto_server_config.proto
+++ b/quic/core/proto/crypto_server_config.proto
@@ -19,7 +19,7 @@
   // private key is specific to the algorithm in question.
   message PrivateKey {
     required uint32 tag = 1;
-    required string private_key = 2;
+    required bytes private_key = 2;
   }
   repeated PrivateKey key = 2;