diff --git a/pre_commit_hooks/util.py b/pre_commit_hooks/util.py
index d68e769..3b960e3 100644
--- a/pre_commit_hooks/util.py
+++ b/pre_commit_hooks/util.py
@@ -12,9 +12,8 @@
 
 
 def added_files():  # type: () -> Set[str]
-    return set(cmd_output(
-        'git', 'diff', '--staged', '--name-only', '--diff-filter=A',
-    ).splitlines())
+    cmd = ('git', 'diff', '--staged', '--name-only', '--diff-filter=A')
+    return set(cmd_output(*cmd).splitlines())
 
 
 def cmd_output(*cmd, **kwargs):  # type: (*str, **Any) -> str