diff --git a/src/boutdata/data.py b/src/boutdata/data.py
index 247dc3dd3..222cf26d1 100644
--- a/src/boutdata/data.py
+++ b/src/boutdata/data.py
@@ -1628,6 +1628,13 @@ def _collect_parallel(self, varname):
             self._shared_buffer[global_slices].copy(), attributes=var_attributes
         )
 
+    def __getstate__(self):
+        new = self.__dict__.copy()
+        new.pop("_file0")
+        new.pop("_root_file")
+        new.pop("_workers")
+        return new
+
     def _worker_function(self, connection, proc_list, shared_buffer_raw):
         data_files = [DataFile(self._file_list[i]) for i in proc_list]
         dim_sizes = tuple(self.grid_info["sizes"][d] for d in ("t", "x", "y", "z"))