diff --git a/Library/Homebrew/os.rb b/Library/Homebrew/os.rb
index 17e9076dca..34c0db2286 100644
--- a/Library/Homebrew/os.rb
+++ b/Library/Homebrew/os.rb
@@ -40,7 +40,7 @@ module OS
   # @api public
   sig { returns(String) }
   def self.uname
-    @uname ||= Utils.safe_popen_read("uname").chomp
+    @uname ||= Utils.safe_popen_read("uname", "-s").chomp
   end
 
   ::OS_VERSION = ENV["HOMEBREW_OS_VERSION"]