diff --git a/lib/ZnapZend/Config.pm b/lib/ZnapZend/Config.pm
index d17a4921..215df97a 100644
--- a/lib/ZnapZend/Config.pm
+++ b/lib/ZnapZend/Config.pm
@@ -179,7 +179,7 @@ my $checkBackupSets = sub {
         if ($backupSet->{src_mbuffer}) {
             if ($backupSet->{src_mbuffer} ne 'off' and !($self->zfs->fileExistsAndExec($backupSet->{src_mbuffer}))) {
                 warn "*** WARNING: executable '$backupSet->{src_mbuffer}' does not exist on source system, will ignore\n\n";
-                $backupSet->{src_mbuffer} = undef;
+                $backupSet->{src_mbuffer} = 'off';
             }
         }
         if (!exists($backupSet->{src_mbuffer_size}) or !($backupSet->{src_mbuffer_size})) {