diff --git a/tqdm/_utils.py b/tqdm/_utils.py
index f5626fec..51b2e5f8 100755
--- a/tqdm/_utils.py
+++ b/tqdm/_utils.py
@@ -41,11 +41,11 @@ def _environ_cols_wrapper():  # pragma: no cover
     import platform
     current_os = platform.system()
     _environ_cols = None
-    if current_os in {'Windows', 'cli'}:
+    if current_os in ['Windows', 'cli']:
         _environ_cols = _environ_cols_windows
         if _environ_cols is None:
             _environ_cols = _environ_cols_tput
-    if current_os in {'Linux', 'Darwin', 'SunOS', 'FreeBSD'} or \
+    if current_os in ['Linux', 'Darwin', 'SunOS', 'FreeBSD'] or \
             current_os.startswith('CYGWIN'):
         _environ_cols = _environ_cols_linux
     return _environ_cols