diff --git a/lib/fluent/plugin/in_kubernetes_metrics.rb b/lib/fluent/plugin/in_kubernetes_metrics.rb
index 0a96105..661c824 100644
--- a/lib/fluent/plugin/in_kubernetes_metrics.rb
+++ b/lib/fluent/plugin/in_kubernetes_metrics.rb
@@ -138,7 +138,7 @@ def init_without_kubeconfig(_options = {})
 
         # Use SSL certificate and bearer token from Kubernetes service account.
         if Dir.exist?(@secret_dir)
-          secret_ca_file = File.join(@secret_dir, 'ca.cert')
+          secret_ca_file = File.join(@secret_dir, 'ca.crt')
           secret_token_file = File.join(@secret_dir, 'token')
 
           if @ca_file.nil? && File.exist?(secret_ca_file)