diff --git a/locals.tf b/locals.tf
index b869920..a741a93 100644
--- a/locals.tf
+++ b/locals.tf
@@ -1,7 +1,7 @@
 locals {
   execution_role_arn = var.create_iam_role ? aws_iam_role.mwaa[0].arn : var.execution_role_arn
 
-  security_group_ids = var.create_security_group ? [aws_security_group.mwaa[0].id] : var.security_group_ids
+  security_group_ids = var.create_security_group ? concat([aws_security_group.mwaa[0].id], var.security_group_ids) : var.security_group_ids
 
   source_bucket_arn = var.create_s3_bucket ? aws_s3_bucket.mwaa[0].arn : var.source_bucket_arn