diff --git a/Lib/idlelib/configHelpSourceEdit.py b/Lib/idlelib/configHelpSourceEdit.py
index 3db1e0a..8924f79 100644
--- a/Lib/idlelib/configHelpSourceEdit.py
+++ b/Lib/idlelib/configHelpSourceEdit.py
@@ -151,6 +151,7 @@
                     pass
                 else:
                     # Mac Safari insists on using the URI form for local files
+                    self.result = list(self.result)
                     self.result[1] = "file://" + path
             self.destroy()