diff --git a/tests/zxcvbn_test.py b/tests/zxcvbn_test.py
index 6752c1f..a33c8dd 100644
--- a/tests/zxcvbn_test.py
+++ b/tests/zxcvbn_test.py
@@ -46,3 +46,13 @@ def test_empty_password():
       zxcvbn(password, user_inputs=[input_])
     except IndexError as ie:
         assert False, "Empty password raised IndexError"
+
+
+def test_user_inputs_side_effects():
+    password = '7r3iz3|)0uz3'
+    input_ = [password]
+
+    guess1 = zxcvbn(password)['guesses_log10']
+    zxcvbn('somepassword', user_inputs=input_)
+    guess2 = zxcvbn(password)['guesses_log10']
+    assert abs(guess1 - guess2) < 1
diff --git a/zxcvbn/matching.py b/zxcvbn/matching.py
index e211ab3..1f43349 100644
--- a/zxcvbn/matching.py
+++ b/zxcvbn/matching.py
@@ -2,6 +2,7 @@
 from . import adjacency_graphs
 import re
 import functools
+import copy
 
 from zxcvbn.scoring import most_guessable_match_sequence
 
@@ -98,7 +99,8 @@ def wrapper(*args, **kwargs):
 # omnimatch -- perform all matches
 @ensure_ranked_dictionaries
 def omnimatch(password, _ranked_dictionaries=None, user_inputs=[]):
-    if len(user_inputs):
+    if _ranked_dictionaries is not None and user_inputs:
+        _ranked_dictionaries = copy.copy(_ranked_dictionaries)
         _ranked_dictionaries['user_inputs'] = build_ranked_dict(user_inputs)
 
     matches = []