diff --git a/variables.tf b/variables.tf
index 2cfb28f..ed42eb4 100644
--- a/variables.tf
+++ b/variables.tf
@@ -18,7 +18,7 @@ variable "additional_thumbprints" {
   type        = list(string)
 
   validation {
-    condition     = length(var.additional_thumbprints) <= 4
+    condition     = var.additional_thumbprints == null ? true : length(var.additional_thumbprints) <= 4
     error_message = "Only 4 additional thumbprints can be set, for a maximum of 5 in the OIDC provider."
   }
 }