diff --git a/PVE/Jobs/Plugin.pm b/PVE/Jobs/Plugin.pm
index 69c31cf2..9cf7f98d 100644
--- a/PVE/Jobs/Plugin.pm
+++ b/PVE/Jobs/Plugin.pm
@@ -52,6 +52,21 @@ sub parse_config {
    return $cfg;
 }
 
+# call the plugin specific decode/encode code
+sub decode_value {
+    my ($class, $type, $key, $value) = @_;
+
+    my $plugin = __PACKAGE__->lookup($type);
+    return $plugin->decode_value($type, $key, $value);
+}
+
+sub encode_value {
+    my ($class, $type, $key, $value) = @_;
+
+    my $plugin = __PACKAGE__->lookup($type);
+    return $plugin->encode_value($type, $key, $value);
+}
+
 sub run {
     my ($class, $cfg) = @_;
     # implement in subclass
diff --git a/PVE/Jobs/VZDump.pm b/PVE/Jobs/VZDump.pm
index 043b7ace..87733e74 100644
--- a/PVE/Jobs/VZDump.pm
+++ b/PVE/Jobs/VZDump.pm
@@ -7,6 +7,7 @@ use PVE::INotify;
 use PVE::VZDump::Common;
 use PVE::API2::VZDump;
 use PVE::Cluster;
+use PVE::JSONSchema;
 
 use base qw(PVE::Jobs::Plugin);
 
@@ -36,6 +37,32 @@ sub options {
     return $options;
 }
 
+sub decode_value {
+    my ($class, $type, $key, $value) = @_;
+
+    if ($key eq 'prune-backups' && !ref($value)) {
+	$value = PVE::JSONSchema::parse_property_string(
+	    'prune-backups',
+	    $value,
+	);
+    }
+
+    return $value;
+}
+
+sub encode_value {
+    my ($class, $type, $key, $value) = @_;
+
+    if ($key eq 'prune-backups' && ref($value) eq 'HASH') {
+	$value = PVE::JSONSchema::print_property_string(
+	    $value,
+	    'prune-backups',
+	);
+    }
+
+    return $value;
+}
+
 sub run {
     my ($class, $conf) = @_;