diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 9999b83e..4e8fb205 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -4366,7 +4366,7 @@ sub vmconfig_update_disk {
 		    # update existing disk
 
 		    # skip non hotpluggable value
-		    if (&$safe_num_ne($drive->{discard}, $old_drive->{discard}) ||
+		    if (&$safe_string_ne($drive->{discard}, $old_drive->{discard}) ||
 			&$safe_string_ne($drive->{iothread}, $old_drive->{iothread}) ||
 			&$safe_string_ne($drive->{queues}, $old_drive->{queues}) ||
 			&$safe_string_ne($drive->{cache}, $old_drive->{cache})) {