diff --git a/ci.jenkins.io.tf b/ci.jenkins.io.tf
index d882109f..f3a88c92 100644
--- a/ci.jenkins.io.tf
+++ b/ci.jenkins.io.tf
@@ -170,7 +170,7 @@ resource "azurerm_network_security_rule" "deny_all_outbound_from_ci_controller_s
   protocol                    = "*"
   source_port_range           = "*"
   destination_port_range      = "*"
-  source_address_prefixes     = "VirtualNetwork"
+  source_address_prefix       = "VirtualNetwork"
   destination_address_prefix  = "*"
   resource_group_name         = azurerm_resource_group.ci_jenkins_io_controller.name
   network_security_group_name = azurerm_network_security_group.ci_jenkins_io_controller.name