diff --git a/lib/Slic3r.pm b/lib/Slic3r.pm
index a3761ac6b..aac355b36 100644
--- a/lib/Slic3r.pm
+++ b/lib/Slic3r.pm
@@ -86,7 +86,12 @@ sub parallelize {
         my $q = Thread::Queue->new;
         $q->enqueue(@items, (map undef, 1..$Config->threads));
         
-        my $thread_cb = sub { $params{thread_cb}->($q) };
+        my $thread_cb = sub {
+            my $result = $params{thread_cb}->($q);
+            Slic3r::thread_cleanup();
+            return $result;
+        };
+            
         @_ = ();
         foreach my $th (map threads->create($thread_cb), 1..$Config->threads) {
             $params{collect_cb}->($th->join);
@@ -96,6 +101,18 @@ sub parallelize {
     }
 }
 
+# call this at the very end of each thread (except the main one)
+# so that it does not try to free existing objects.
+# at that stage, existing objects are only those that we 
+# inherited at the thread creation (thus shared) and those 
+# that we are returning: destruction will be handled by the
+# main thread in both cases.
+sub thread_cleanup {
+    # prevent destruction of shared objects
+    no warnings 'redefine';
+    *Slic3r::Object::XS::ZTable::DESTROY    = sub {};
+}
+
 sub encode_path {
     my ($filename) = @_;
     return encode('locale_fs', $filename);