diff --git a/ratis-client/src/main/java/org/apache/ratis/client/impl/OrderedAsync.java b/ratis-client/src/main/java/org/apache/ratis/client/impl/OrderedAsync.java
index 791adc8982..f63266544a 100644
--- a/ratis-client/src/main/java/org/apache/ratis/client/impl/OrderedAsync.java
+++ b/ratis-client/src/main/java/org/apache/ratis/client/impl/OrderedAsync.java
@@ -114,7 +114,7 @@ public void fail(Throwable e) {
 
     @Override
     public String toString() {
-      return "[cid=" + callId + ", seq=" + getSeqNum() + "]";
+      return "[cid=" + callId + ", seq=" + getSeqNum() + (isFirst? "(1st)": "") + "]";
     }
   }
 
@@ -201,7 +201,8 @@ private void sendRequestWithRetry(PendingOrderedRequest pending) {
     }
 
     if (getSlidingWindow(request).isFirst(pending.getSeqNum())) {
-      pending.setFirstRequest();
+      Preconditions.assertTrue(request.getSlidingWindowEntry().getIsFirst(),
+          () -> "The first request is not marked as first: " + request);
     }
     LOG.debug("{}: send* {}", client.getId(), request);
     client.getClientRpc().sendRequestAsync(request).thenAccept(reply -> {
diff --git a/ratis-common/src/main/java/org/apache/ratis/util/ProtoUtils.java b/ratis-common/src/main/java/org/apache/ratis/util/ProtoUtils.java
index 161715bf80..29ee24f51c 100644
--- a/ratis-common/src/main/java/org/apache/ratis/util/ProtoUtils.java
+++ b/ratis-common/src/main/java/org/apache/ratis/util/ProtoUtils.java
@@ -239,7 +239,7 @@ static String toString(SlidingWindowEntry proto) {
     if (proto == null) {
       return null;
     }
-    return proto.getSeqNum() + (proto.getIsFirst()? "*": "");
+    return proto.getSeqNum() + (proto.getIsFirst()? "(1st)": "");
   }
 
   static String toString(RaftRpcRequestProto proto) {