diff --git a/CHANGELOG.asciidoc b/CHANGELOG.asciidoc
index dd230fb5a406..a6856b4c1c2c 100644
--- a/CHANGELOG.asciidoc
+++ b/CHANGELOG.asciidoc
@@ -67,6 +67,7 @@ https://github.com/elastic/beats/compare/v6.0.0-beta2...master[Check the HEAD di
 - Add raw JSON to message field when JSON parsing fails. {issue}6516[6516]
 
 *Heartbeat*
+- Fix race due to updates of shared a map, that was not supposed to be shared between multiple go-routines. {issue}6616[6616]
 
 *Metricbeat*
 
diff --git a/heartbeat/monitors/util.go b/heartbeat/monitors/util.go
index 88b58984e2ff..efd6c7551964 100644
--- a/heartbeat/monitors/util.go
+++ b/heartbeat/monitors/util.go
@@ -122,6 +122,8 @@ func annotated(
 		}
 
 		if fields != nil {
+			fields = fields.Clone()
+
 			status := look.Status(err)
 			fields.DeepUpdate(common.MapStr{
 				"monitor": common.MapStr{
@@ -130,7 +132,7 @@ func annotated(
 				},
 			})
 			if user := settings.Fields; user != nil {
-				fields.DeepUpdate(user)
+				fields.DeepUpdate(user.Clone())
 			}
 
 			event.Timestamp = start
@@ -370,10 +372,13 @@ func resolveErr(host string, err error) (common.MapStr, []TaskRunner, error) {
 func WithFields(fields common.MapStr, r TaskRunner) TaskRunner {
 	return MakeCont(func() (common.MapStr, []TaskRunner, error) {
 		event, cont, err := r.Run()
-		if event == nil {
+		if event != nil {
+			event = event.Clone()
+			event.DeepUpdate(fields)
+		} else if err != nil {
 			event = common.MapStr{}
+			event.DeepUpdate(fields)
 		}
-		event.DeepUpdate(fields)
 
 		for i := range cont {
 			cont[i] = WithFields(fields, cont[i])