1 files changed, 1 insertions, 1 deletions
diff --git a/coverage/files.py b/coverage/files.py
index 08ce1e84..72c0bf92 100644
--- a/coverage/files.py
+++ b/coverage/files.py
@@ -147,7 +147,7 @@ def prep_patterns(patterns):
 class TreeMatcher(object):
     """A matcher for files in a tree."""
     def __init__(self, directories):
-        self.dirs = directories[:]
+        self.dirs = list(directories)
 
     def __repr__(self):
         return "<TreeMatcher %r>" % self.dirs