diff --git a/newrelic/structures_newrelic_alert_muting_rule.go b/newrelic/structures_newrelic_alert_muting_rule.go
index ca80009da..089976fb1 100644
--- a/newrelic/structures_newrelic_alert_muting_rule.go
+++ b/newrelic/structures_newrelic_alert_muting_rule.go
@@ -278,7 +278,11 @@ func flattenMutingRule(mutingRule *alerts.MutingRule, d *schema.ResourceData) er
 	configuredCondition := x.([]interface{})
 
 	_ = d.Set("enabled", mutingRule.Enabled)
-	_ = d.Set("action_on_muting_rule_window_ended", mutingRule.ActionOnMutingRuleWindowEnded)
+
+	if _, ok := d.GetOk("action_on_muting_rule_window_ended"); ok {
+		_ = d.Set("action_on_muting_rule_window_ended", mutingRule.ActionOnMutingRuleWindowEnded)
+	}
+
 	err := d.Set("condition", flattenMutingRuleConditionGroup(mutingRule.Condition, configuredCondition))
 	if err != nil {
 		return nil