diff --git a/pandora_server/lib/PandoraFMS/DiscoveryServer.pm b/pandora_server/lib/PandoraFMS/DiscoveryServer.pm
index f17d2c5363..a556334ee0 100644
--- a/pandora_server/lib/PandoraFMS/DiscoveryServer.pm
+++ b/pandora_server/lib/PandoraFMS/DiscoveryServer.pm
@@ -433,7 +433,7 @@ sub PandoraFMS::Recon::Base::guess_os($$;$) {
     return OS_OTHER if ($? != 0);
     my $str_os;
     if ($return =~ /Aggressive OS guesses:\s*(.*)|OS details:\s(.*)/) {
-      if($1 ne "") {
+      if(defined($1) && $1 ne "") {
         $str_os = $1;
       } else {
         $str_os = $2;