diff --git a/ext_open/util.py b/ext_open/util.py
index 8ce862a..22c5074 100644
--- a/ext_open/util.py
+++ b/ext_open/util.py
@@ -18,7 +18,7 @@ def get_drives():
     bitmask = windll.kernel32.GetLogicalDrives()
     for letter in uppercase:
         if bitmask & 1:
-            drives.append(f'{letter}:\\')
+            drives.append('{letter}:\\'.format(letter=letter)
         bitmask >>= 1
 
     return drives