diff --git a/bilby/core/prior/dict.py b/bilby/core/prior/dict.py
index 094625445574fd3e131099ed65d805ab4ab449dc..85e8ac4ef75c8808fd20f1b175fd5214364deb1a 100644
--- a/bilby/core/prior/dict.py
+++ b/bilby/core/prior/dict.py
@@ -1,4 +1,3 @@
-import copy
 import json
 import os
 import re
@@ -208,7 +207,8 @@ class PriorDict(dict):
 
     def from_dictionary(self, dictionary):
         mvgkwargs = {}
-        for key, val in copy.deepcopy(dictionary).items():
+        for key in list(dictionary.keys()):
+            val = dictionary[key]
             if isinstance(val, Prior):
                 continue
             elif isinstance(val, (int, float)):