diff --git a/call.go b/call.go
index ebfffdd6..4efc5bdd 100644
--- a/call.go
+++ b/call.go
@@ -64,23 +64,24 @@ func recvResponse(dopts dialOptions, t transport.ClientTransport, c *callInfo, s
 		return
 	}
 	p := &parser{r: stream}
-	var inStats *stats.InPayload
+	var inPayload *stats.InPayload
 	if stats.On() {
-		inStats = &stats.InPayload{
+		inPayload = &stats.InPayload{
 			Client: true,
 		}
 	}
 	for {
-		if err = recv(p, dopts.codec, stream, dopts.dc, reply, math.MaxInt32, inStats); err != nil {
+		if err = recv(p, dopts.codec, stream, dopts.dc, reply, math.MaxInt32, inPayload); err != nil {
 			if err == io.EOF {
 				break
 			}
 			return
 		}
 	}
-	if err == io.EOF && stream.StatusCode() == codes.OK && inStats != nil {
-		// TODO in the current implementation, inTrailer is handled before inStats. Fix the order if necessary.
-		stats.Handle(stream.Context(), inStats)
+	if inPayload != nil && err == io.EOF && stream.StatusCode() == codes.OK {
+		// TODO in the current implementation, inTrailer may be handled before inStats in some cases.
+		// Fix the order if necessary.
+		stats.Handle(stream.Context(), inPayload)
 	}
 	c.trailerMD = stream.Trailer()
 	return nil
@@ -101,25 +102,25 @@ func sendRequest(ctx context.Context, codec Codec, compressor Compressor, callHd
 		}
 	}()
 	var (
-		cbuf     *bytes.Buffer
-		outStats *stats.OutPayload
+		cbuf       *bytes.Buffer
+		outPayload *stats.OutPayload
 	)
 	if compressor != nil {
 		cbuf = new(bytes.Buffer)
 	}
 	if stats.On() {
-		outStats = &stats.OutPayload{
+		outPayload = &stats.OutPayload{
 			Client: true,
 		}
 	}
-	outBuf, err := encode(codec, args, compressor, cbuf, outStats)
+	outBuf, err := encode(codec, args, compressor, cbuf, outPayload)
 	if err != nil {
 		return nil, Errorf(codes.Internal, "grpc: %v", err)
 	}
 	err = t.Write(stream, outBuf, opts)
-	if outStats != nil {
-		outStats.SentTime = time.Now()
-		stats.Handle(stream.Context(), outStats)
+	if outPayload != nil {
+		outPayload.SentTime = time.Now()
+		stats.Handle(stream.Context(), outPayload)
 	}
 	// t.NewStream(...) could lead to an early rejection of the RPC (e.g., the service/method
 	// does not exist.) so that t.Write could get io.EOF from wait(...). Leave the following
diff --git a/stats/stats.go b/stats/stats.go
index e7094c1c..7b8ee123 100644
--- a/stats/stats.go
+++ b/stats/stats.go
@@ -187,10 +187,10 @@ var (
 
 // On indicates whether stats is started.
 func On() bool {
-	return atomic.LoadInt32(on) == 1
+	return atomic.CompareAndSwapInt32(on, 1, 1)
 }
 
-// Handle returns the call back function registered by user to process the stats.
+// Handle processes the stats using the call back function registered by user.
 func Handle(ctx context.Context, s RPCStats) {
 	handler(ctx, s)
 }
@@ -202,8 +202,7 @@ func RegisterHandler(f func(context.Context, RPCStats)) {
 	handler = f
 }
 
-// Start starts the stats collection.
-// Stats will only be started if handler is not nil.
+// Start starts the stats collection and reporting if there is a registered stats handle.
 func Start() {
 	if handler == nil {
 		grpclog.Println("handler is nil when starting stats. Stats is not started")
@@ -212,8 +211,8 @@ func Start() {
 	atomic.StoreInt32(on, 1)
 }
 
-// Stop stops the collection of any further stats.
-// Stop won't unregister handler.
+// Stop stops the stats collection and processing.
+// Stop does not unregister handler.
 func Stop() {
 	atomic.StoreInt32(on, 0)
 }