diff --git a/tangos/input_handlers/pynbody.py b/tangos/input_handlers/pynbody.py
index 8bdaf23e..3508b207 100644
--- a/tangos/input_handlers/pynbody.py
+++ b/tangos/input_handlers/pynbody.py
@@ -98,6 +98,7 @@ def load_timestep_without_caching(self, ts_extension, mode=None) -> pynbody.snap
             raise NotImplementedError("Load mode %r is not implemented"%mode)
 
     def _build_kdtree(self, timestep, mode):
+        timestep.wrap() # Because we have converted pos to kpc, FP roundoff may place particles at the boundaries outside the period of the box.
         timestep.build_tree()
 
     def load_region(self, ts_extension, region_specification, mode=None, expected_number_of_queries=None) -> pynbody.snapshot.simsnap.SimSnap:
diff --git a/tangos/parallel_tasks/pynbody_server/snapshot_queue.py b/tangos/parallel_tasks/pynbody_server/snapshot_queue.py
index 9982d1c5..b4fdf46a 100644
--- a/tangos/parallel_tasks/pynbody_server/snapshot_queue.py
+++ b/tangos/parallel_tasks/pynbody_server/snapshot_queue.py
@@ -110,6 +110,7 @@ def build_tree(self):
                 num_threads = multiprocessing.cpu_count()
             else:
                 num_threads = None
+            self.current_snapshot.wrap() # Because we have converted pos to kpc, FP roundoff may place particles at the boundaries outside the period of the box.
             self.current_snapshot.build_tree(num_threads=num_threads,
                                              shared_mem=self.current_shared_mem_flag)