diff --git a/lib/Simba/CA.pm b/lib/Simba/CA.pm
index e3ac2b1..3405c96 100644
--- a/lib/Simba/CA.pm
+++ b/lib/Simba/CA.pm
@@ -153,13 +153,7 @@ sub run {
 sub backup2disk {
     my ($self, $target) = @_;
 
-    # XXX - lock fileset here, we don't want to backup the same fileset twice concurrently.
-    # theoretically something like
-    $self->{dbh}->selectall_arrayref(q{select * from filesets where id = ? for update}, {}, $target->{id});
-    # should suffice, but I'm not sure if that blocks too much (does that block reads? block the whole table?)
-    # Just try it and we will see ...
-    # According to the manual this only works if autocommit is off, so it probably doesn't work on MyISAM
-    # anyway.
+    $self->reserve_fileset($target);
 
     $self->log(3, "starting backup for target host " . $target->{host} . " dir " . $target->{dir});
     $self->{target} = $target;
@@ -215,10 +209,36 @@ sub backup2disk {
     }
     $self->flush_insert_instances();
     $self->close_session();
+    $self->reserve_fileset($target);
     $self->log(3, "finished backup for target host " . $target->{host} . " dir " . $target->{dir} . ": $count files");
     $self->{counts}{objects} += $count;
 }
 
+sub reserve_fileset {
+    my ($self, $target) = @_;
+
+    for (;;) {
+        my $rows = $self->{dbh}->do(q{update filesets set pid=? where id = ? and pid is null}, {}, $$, $target->{id});
+        return if $rows == 1;
+        my $pid = $self->{dbh}->selectrow_array(q{select pid from filesets where id = ?}, {}, $target->{id});
+        $self->log(3, "fileset $target->{id} appears to be in use by my pid $pid");
+        if (!kill(0, $pid) && $!{ESRCH}) {
+            $self->log(3, "pid $pid doesn't exist, trying to release fileset $target->{id}");
+            $self->{dbh}->do(q{update filesets set pid=null where id = ? and pid=?}, {}, $target->{id}, $pid);
+        }
+        sleep 60;
+    }
+}
+
+
+sub release_fileset {
+    my ($self, $target) = @_;
+
+    $self->log(3, "releasing fileset $target->{id}");
+    $self->{dbh}->do(q{update filesets set pid=null where id=? and pid=?}, {}, $target->{id}, $$);
+}
+
+
 sub parse {
     my ($self, $s) = @_;