if fork() fails, it returns undef

if fork() fails, it returns undef not a negative number

1 files changed, 1 insertions, 1 deletions

diff --git a/apt-mirror b/apt-mirror
index 20d3559..e6b4b0b 100755
--- a/apt-mirror
+++ b/apt-mirror
@@ -249,7 +249,7 @@ sub download_urls
 
         $pid = fork();
 
-        die("apt-mirror: can't do fork in download_urls") if $pid < 0;
+        die("apt-mirror: can't do fork in download_urls") if !defined($pid);
 
         if ( $pid == 0 )
         {