diff --git a/src/PVE/VZDump/LXC.pm b/src/PVE/VZDump/LXC.pm
index 9bf95af..014d72b 100644
--- a/src/PVE/VZDump/LXC.pm
+++ b/src/PVE/VZDump/LXC.pm
@@ -157,6 +157,10 @@ sub prepare {
 
         next if !$volid || !$mount;
 
+        # the path of a mount point is always relative to the root of the container, but it
+        # does not need to start with a slash, which all the paths built below rely on
+        $mount = $volume_config->{mp} = "/$mount" if $mount !~ m!^/!;
+
         if (!$included) {
             my $type = $volume_config->{type};
             push @$exclude_dirs, $mount;