diff --git a/src/PVE/INotify.pm b/src/PVE/INotify.pm
index 4f682be..ad45cd2 100644
--- a/src/PVE/INotify.pm
+++ b/src/PVE/INotify.pm
@@ -1265,8 +1265,10 @@ sub __interface_to_string {
 
 	$v = defined($d->{bridge_fd}) ? $d->{bridge_fd} : 0;
 	# 0 is only allowed when STP is disabled
-	if ($v || $no_stp) {
+	if ($no_stp || ($v >= 2 && $v <= 30)) {
 	    $raw .= "\tbridge-fd $v\n";
+	} else {
+	    warn "'$iface': not setting 'bridge_fd' to value '$v' outside of allowed range 2-30\n";
 	}
 	$done->{bridge_fd} = 1;