diff --git a/git_command.py b/git_command.py
index 4aeacd5..513b9eb 100644
--- a/git_command.py
+++ b/git_command.py
@@ -127,7 +127,7 @@
                ssh_proxy = False,
                cwd = None,
                gitdir = None):
-    env = dict(os.environ)
+    env = os.environ.copy()
 
     for e in [REPO_TRACE,
               GIT_DIR,