diff --git a/tensorflow/compiler/xla/service/hlo.proto b/tensorflow/compiler/xla/service/hlo.proto
index c4911df150f..134c8953b15 100644
--- a/tensorflow/compiler/xla/service/hlo.proto
+++ b/tensorflow/compiler/xla/service/hlo.proto
@@ -171,7 +171,7 @@ message HloInstructionProto {
   xla.OpSharding sharding = 40;
 
   // Backend configuration for the instruction. Has backend-specific meaning.
-  string backend_config = 43;
+  bytes backend_config = 43;
 
   // Cross replica op fields.
   repeated ReplicaGroup replica_groups = 49;