diff --git a/src/PVE/ACME/DNSChallenge.pm b/src/PVE/ACME/DNSChallenge.pm
index 9b28970..7214d88 100644
--- a/src/PVE/ACME/DNSChallenge.pm
+++ b/src/PVE/ACME/DNSChallenge.pm
@@ -23,13 +23,19 @@ sub type {
 }
 
 my $DNS_API_CHALLENGE_SCHEMA_FN = '/usr/share/proxmox-acme/dns-challenge-schema.json';
-my $plugins = from_json(PVE::Tools::file_get_contents($DNS_API_CHALLENGE_SCHEMA_FN));
 
+my $plugin_cache;
 sub get_supported_plugins {
-    return $plugins;
+    if (!$plugin_cache) {
+	$plugin_cache = -e $DNS_API_CHALLENGE_SCHEMA_FN # we allow this to be optional as not all users require
+	    ? from_json(PVE::Tools::file_get_contents($DNS_API_CHALLENGE_SCHEMA_FN))
+	    : {};
+    }
+    return $plugin_cache;
 }
 
 sub properties {
+    my $plugins = get_supported_plugins();
     return {
 	api => {
 	    description => "API plugin name",