diff --git a/snapshotprocessor.py b/snapshotprocessor.py
index 5ffb6fc..072a3ed 100644
--- a/snapshotprocessor.py
+++ b/snapshotprocessor.py
@@ -1371,9 +1371,10 @@ class SnapshotProcessor(HDF5Container):
             df = pd.read_csv(csv_name, header=None, names=header)
         return {key: df[key].values for key in df}
 
-    def _pspec(self, **kwargs):
+    def _pspec(self, overwrite_file=False, **kwargs):
         outfile = self.pspec_filename
-        pspec_new.pspec(repo=self.path, iouts=[self.num], outfile=outfile, **kwargs)
+        if overwrite_file or not os.path.exists(self.pspec_filename):
+          pspec_new.pspec(repo=self.path, iouts=[self.num], outfile=outfile, **kwargs)
         return np.array([self.pspec_filename])
 
     def _write_particles(self):