diff --git a/src/PVE/RESTEnvironment.pm b/src/PVE/RESTEnvironment.pm
index 91de875..871f12b 100644
--- a/src/PVE/RESTEnvironment.pm
+++ b/src/PVE/RESTEnvironment.pm
@@ -525,7 +525,7 @@ sub fork_worker {
 		    if !open(STDIN, "</dev/null");
 
 		$outfh = PVE::Tools::upid_open($upid);
-		$resfh = $outfh;
+		$resfh = fileno($outfh);
 	    }