diff --git a/Library/Homebrew/cxxstdlib.rb b/Library/Homebrew/cxxstdlib.rb
index e863b226bb..8b259144a8 100644
--- a/Library/Homebrew/cxxstdlib.rb
+++ b/Library/Homebrew/cxxstdlib.rb
@@ -1,23 +1,30 @@
-# typed: true # rubocop:todo Sorbet/StrictSigil
+# typed: strong
 # frozen_string_literal: true
 
 require "compilers"
 
 # Combination of C++ standard library and compiler.
 class CxxStdlib
+  sig { params(type: T.nilable(Symbol), compiler: T.any(Symbol, String)).returns(CxxStdlib) }
   def self.create(type, compiler)
     raise ArgumentError, "Invalid C++ stdlib type: #{type}" if type && [:libstdcxx, :libcxx].exclude?(type)
 
     CxxStdlib.new(type, compiler)
   end
 
-  attr_reader :type, :compiler
+  sig { returns(T.nilable(Symbol)) }
+  attr_reader :type
 
+  sig { returns(Symbol) }
+  attr_reader :compiler
+
+  sig { params(type: T.nilable(Symbol), compiler: T.any(Symbol, String)).void }
   def initialize(type, compiler)
     @type = type
-    @compiler = compiler.to_sym
+    @compiler = T.let(compiler.to_sym, Symbol)
   end
 
+  sig { returns(String) }
   def type_string
     type.to_s.gsub(/cxx$/, "c++")
   end