diff --git a/spacy/cli/download.py b/spacy/cli/download.py
index 85aaf3e5b..80c2432c3 100644
--- a/spacy/cli/download.py
+++ b/spacy/cli/download.py
@@ -128,6 +128,6 @@ def get_version(model, comp):
 
 def download_model(filename, user_pip_args=None):
     download_url = about.__download_url__ + "/" + filename
-    pip_args = user_pip_args if user_pip_args is not None else []
+    pip_args = list(user_pip_args) if user_pip_args is not None else []
     cmd = [sys.executable, "-m", "pip", "install"] + pip_args + [download_url]
     return subprocess.call(cmd, env=os.environ.copy())