diff --git a/rauth/utils.py b/rauth/utils.py
index b0b420a..0746b2d 100644
--- a/rauth/utils.py
+++ b/rauth/utils.py
@@ -23,7 +23,9 @@ def absolute_url(url):
 def parse_utf8_qsl(s):
     d = dict(parse_qsl(s))
 
-    for k, v in d.items():  # pragma: no cover
+    copy_d = dict(d);
+
+    for k, v in copy_d.items():  # pragma: no cover
         if not isinstance(k, bytes) and not isinstance(v, bytes):
             # skip this iteration if we have no keys or values to update
             continue
@@ -36,6 +38,7 @@ def parse_utf8_qsl(s):
     return d
 
 
+
 def get_sorted_params(params):
     def sorting_gen():
         for k in sorted(params.keys()):