diff --git a/argocd/prometheus/test/argocd_values.yaml b/argocd/prometheus/test/argocd_values.yaml
index 7fe4828..ba03617 100644
--- a/argocd/prometheus/test/argocd_values.yaml
+++ b/argocd/prometheus/test/argocd_values.yaml
@@ -3,6 +3,9 @@ kube-prometheus-stack:
     admissionWebhooks:
       certManager:
         enabled: true
+        issuerRef:
+          name: "lets-encrypt"
+          kind: "ClusterIssuer"
   prometheus-node-exporter:
     hostRootFsMount:
       mountPropagation: None