diff --git a/src/core/census/grpc_filter.c b/src/core/census/grpc_filter.c
index 76b72573782..4529ae9bd7e 100644
--- a/src/core/census/grpc_filter.c
+++ b/src/core/census/grpc_filter.c
@@ -115,7 +115,10 @@ static void server_mutate_op(grpc_call_element *elem,
 static void server_start_transport_op(grpc_exec_ctx *exec_ctx,
                                       grpc_call_element *elem,
                                       grpc_transport_stream_op *op) {
-  /* call_data *calld = elem->call_data;
+  /* TODO(ctiller): this code fails. I don't know why. I expect it's
+                    incomplete, and someone should look at it soon.
+
+  call_data *calld = elem->call_data;
   GPR_ASSERT((calld->op_id.upper != 0) || (calld->op_id.lower != 0)); */
   server_mutate_op(elem, op);
   grpc_call_next_op(exec_ctx, elem, op);