diff --git a/common/alerting-message/inputs.tf b/common/alerting-message/inputs.tf
index d113f84..60c1305 100644
--- a/common/alerting-message/inputs.tf
+++ b/common/alerting-message/inputs.tf
@@ -6,13 +6,13 @@ variable "message_alert" {
 variable "message_warning" {
   description = "Define a broadcast channel for warning alerts"
   type        = string
-  default     = "false"
+  default     = null
 }
 
 variable "message_nodata" {
   description = "Define a broadcast channel for nodata alerts"
   type        = string
-  default     = "false"
+  default     = null
 }
 
 variable "prepend_text" {
diff --git a/common/alerting-message/main.tf b/common/alerting-message/main.tf
index 37438c4..a05c986 100644
--- a/common/alerting-message/main.tf
+++ b/common/alerting-message/main.tf
@@ -10,7 +10,7 @@ EOF
 
   vars = {
     message_alert    = var.message_alert
-    message_warning  = var.message_warning == "false" ? var.message_alert : var.message_warning
+    message_warning  = var.message_warning == null ? var.message_alert : var.message_warning
     message_nodata   = var.message_nodata == null ? var.message_alert : var.message_nodata
     message_recovery = join(" ", compact(distinct(list(var.message_alert, var.message_warning, var.message_nodata))))
     prepend_text     = var.prepend_text