diff --git a/Library/Homebrew/os/linux/kernel.rb b/Library/Homebrew/os/linux/kernel.rb
index 0fe09b3952..99add3c083 100644
--- a/Library/Homebrew/os/linux/kernel.rb
+++ b/Library/Homebrew/os/linux/kernel.rb
@@ -1,4 +1,4 @@
-# typed: true
+# typed: strict
 # frozen_string_literal: true
 
 module OS
@@ -14,6 +14,7 @@ module OS
         Version.new "3.2"
       end
 
+      sig { returns(T::Boolean) }
       def below_minimum_version?
         OS.kernel_version < minimum_version
       end