diff --git a/client.go b/client.go
index d5a3023..8ecb87d 100644
--- a/client.go
+++ b/client.go
@@ -55,9 +55,12 @@ func (c *Client) Run(res chan *RunResults) {
 			runResults.MsgTimeMin = stats.StatsMin(times)
 			runResults.MsgTimeMax = stats.StatsMax(times)
 			runResults.MsgTimeMean = stats.StatsMean(times)
-			runResults.MsgTimeStd = stats.StatsSampleStandardDeviation(times)
 			runResults.RunTime = duration.Seconds()
 			runResults.MsgsPerSec = float64(runResults.Successes) / duration.Seconds()
+			// calculate std if sample is > 1, otherwise leave as 0 (convention)
+			if c.MsgCount > 1 {
+				runResults.MsgTimeStd = stats.StatsSampleStandardDeviation(times)
+			}
 
 			// report results and exit
 			res <- runResults
@@ -123,8 +126,8 @@ func (c *Client) pubMessages(in, out chan *Message, doneGen, donePub chan bool)
 		SetAutoReconnect(true).
 		SetOnConnectHandler(onConnected).
 		SetConnectionLostHandler(func(client mqtt.Client, reason error) {
-		log.Printf("CLIENT %v lost connection to the broker: %v. Will reconnect...\n", c.ID, reason.Error())
-	})
+			log.Printf("CLIENT %v lost connection to the broker: %v. Will reconnect...\n", c.ID, reason.Error())
+		})
 	if c.BrokerUser != "" && c.BrokerPass != "" {
 		opts.SetUsername(c.BrokerUser)
 		opts.SetPassword(c.BrokerPass)
diff --git a/main.go b/main.go
index 6008ed0..c262233 100644
--- a/main.go
+++ b/main.go
@@ -72,7 +72,11 @@ func main() {
 
 	flag.Parse()
 	if *clients < 1 {
-		log.Fatal("Invlalid arguments")
+		log.Fatalf("Invalid arguments: number of clients should be > 1, given: %v", *clients)
+	}
+
+	if *count < 1 {
+		log.Fatalf("Invalid arguments: messages count should be > 1, given: %v", *count)
 	}
 
 	resCh := make(chan *RunResults)
@@ -101,12 +105,13 @@ func main() {
 		results[i] = <-resCh
 	}
 	totalTime := time.Now().Sub(start)
-	totals := calculateTotalResults(results, totalTime)
+	totals := calculateTotalResults(results, totalTime, *clients)
 
 	// print stats
 	printResults(results, totals, *format)
 }
-func calculateTotalResults(results []*RunResults, totalTime time.Duration) *TotalResults {
+
+func calculateTotalResults(results []*RunResults, totalTime time.Duration, sampleSize int) *TotalResults {
 	totals := new(TotalResults)
 	totals.TotalRunTime = totalTime.Seconds()
 
@@ -138,7 +143,10 @@ func calculateTotalResults(results []*RunResults, totalTime time.Duration) *Tota
 	totals.AvgMsgsPerSec = stats.StatsMean(msgsPerSecs)
 	totals.AvgRunTime = stats.StatsMean(runTimes)
 	totals.MsgTimeMeanAvg = stats.StatsMean(msgTimeMeans)
-	totals.MsgTimeMeanStd = stats.StatsSampleStandardDeviation(msgTimeMeans)
+	// calculate std if sample is > 1, otherwise leave as 0 (convention)
+	if sampleSize > 1 {
+		totals.MsgTimeMeanStd = stats.StatsSampleStandardDeviation(msgTimeMeans)
+	}
 
 	return totals
 }
@@ -150,7 +158,10 @@ func printResults(results []*RunResults, totals *TotalResults, format string) {
 			Runs:   results,
 			Totals: totals,
 		}
-		data, _ := json.Marshal(jr)
+		data, err := json.Marshal(jr)
+		if err != nil {
+			log.Fatalf("Error marshalling results: %v", err)
+		}
 		var out bytes.Buffer
 		json.Indent(&out, data, "", "\t")