diff --git a/Library/Homebrew/os/mac/version.rb b/Library/Homebrew/os/mac/version.rb
index ef173c8ea0..89b5d9b544 100644
--- a/Library/Homebrew/os/mac/version.rb
+++ b/Library/Homebrew/os/mac/version.rb
@@ -14,7 +14,7 @@ module OS
       extend T::Sig
 
       SYMBOLS = {
-        monterey:    "12"
+        monterey:    "12",
         big_sur:     "11",
         catalina:    "10.15",
         mojave:      "10.14",